feat(schema): subtitle/explicit columns, authors+publishers arrays, float series numbers

Phase 1 of the series/collections/metadata overhaul
(~/.opencode/plan/series-collections-metadata-overhaul.md).

Schema (in place, idempotent):
- media_items.series_number INTEGER -> DOUBLE PRECISION: real-world
  ordinals are decimals (0.5, 1.5 novellas); INTEGER silently truncated
  them (calibre 2.5 pinned as 2 in tests).
- + subtitle TEXT, explicit BOOLEAN (sidecar ingest; ABS explicit /
  Audible isAdult).
- + authors/authors_search/publishers/publishers_search TEXT[] NOT NULL
  (narrators A2a precedent). Arrays are write truth; author/publisher
  varchars become trigger-regenerated display strings
  (sync_author_publisher_display) so every varchar consumer (trgm
  search, facets, API, OPDS/Kobo) keeps working unchanged.
- Row-level NULL normalization for the new arrays in
  set_library_type_name (A2 lesson: Go nil -> explicit NULL -> 23502).
- Backfills ARRAY[author]/ARRAY[publisher] — deliberately no
  comma-splitting ('Tolkien, J.R.R.' would corrupt; scanner kept only
  authors[0] historically).
- collection_items.position INTEGER + (collection_id, position) index
  for playlist ordering.

Go: sqlc regen; MediaMetadata/handler params gain Subtitle/Explicit/
Authors/Publishers (legacy singles still accepted, arrays win);
SeriesNumber int32 -> float64 end to end; metadata_overrides adapted
with legacy override keys ('author'/'publisher') preserved so existing
user overrides survive; bulk author edit writes the array.

Pins widened (docs/contract_pins.md): raw sqlc row key set + the six
new columns; changelog entry added.

Verified: unit suite green; integration sweep (bulk/smart collections/
scanner/stats/sync/queue/calibre/pins/audiobooks) green against the
shared dev DB after in-place migration. Pre-existing unrelated red:
TestOwnershipAndAdminTestSuite/TestAdminCreateUser timezone inheritance
fails identically at the pre-change commit (live shared state).

internal/services/media_scanner.go

@@ -49,11 +49,14 @@ import (
 // MediaMetadata contains extracted metadata for media files (ebooks, comics, manga)
 type MediaMetadata struct {
 	Title        string
-	Author       string
+	Subtitle     string
+	Author       string // legacy single-value fill; Authors[] is the write truth
+	Authors      []string
 	Description  string
 	Series       string
-	SeriesNumber int32
-	Publisher    string
+	SeriesNumber float64
+	Publisher    string // legacy single-value fill; Publishers[] is the write truth
+	Publishers   []string
 	PublishDate  time.Time
 	Contributors []string
 	CoverPath    string
@@ -61,6 +64,7 @@ type MediaMetadata struct {
 	ASIN         string
 	Tags         []string
 	Genre        string
+	Explicit     bool
 
 	FileHashInfo *HashInfo
 	FileFormats  []*FormatInfo
@@ -715,8 +719,8 @@ func (s *MediaScanner) extractFolderStructureMetadata(path, rootFolder string) *
 		seriesMatch := regexp.MustCompile(`^(.*),\s+Book\s+#(\d+)\s*-\s*(.*)$`).FindStringSubmatch(possibleSeries)
 		if len(seriesMatch) == 4 {
 			metadata.Series = strings.ReplaceAll(seriesMatch[1], "_", " ")
-			if seriesNum, err := strconv.ParseInt(seriesMatch[2], 10, 32); err == nil {
-				metadata.SeriesNumber = int32(seriesNum)
+			if seriesNum, err := strconv.ParseFloat(seriesMatch[2], 64); err == nil {
+				metadata.SeriesNumber = seriesNum
 			}
 			metadata.Title = strings.ReplaceAll(possibleTitle, "_", " ")
 		} else {
@@ -725,11 +729,11 @@ func (s *MediaScanner) extractFolderStructureMetadata(path, rootFolder string) *
 			metadata.Title = strings.ReplaceAll(possibleTitle, "_", " ")
 
 			// Try to extract series number from title
-			titleNumMatch := regexp.MustCompile(`^(.*)\s+(\d+)$`).FindStringSubmatch(metadata.Title)
+			titleNumMatch := regexp.MustCompile(`^(.*)\s+(\d+(?:\.\d+)?)$`).FindStringSubmatch(metadata.Title)
 			if len(titleNumMatch) == 3 {
 				metadata.Title = titleNumMatch[1]
-				if seriesNum, err := strconv.ParseInt(titleNumMatch[2], 10, 32); err == nil {
-					metadata.SeriesNumber = int32(seriesNum)
+				if seriesNum, err := strconv.ParseFloat(titleNumMatch[2], 64); err == nil {
+					metadata.SeriesNumber = seriesNum
 				}
 			}
 		}
@@ -1009,7 +1013,9 @@ func (s *MediaScanner) processMediaFile(ctx context.Context, path string) (bool,
 	createdItem, err := s.db.CreateMediaItem(ctx, database.CreateMediaItemParams{
 		LibraryID:          libraryID,
 		Title:              metadata.Title,
-		Author:             pgtype.Text{String: metadata.Author, Valid: metadata.Author != ""},
+		Subtitle:           pgtype.Text{String: metadata.Subtitle, Valid: metadata.Subtitle != ""},
+		Authors:            nilToEmpty(utils.SingleOrSlice(metadata.Author, metadata.Authors)),
+		AuthorsSearch:      utils.NormalizeTagsSearch(utils.SingleOrSlice(metadata.Author, metadata.Authors)),
 		Isbn:               pgtype.Text{String: utils.NormalizeISBNSafe(metadata.ISBN), Valid: metadata.ISBN != ""},
 		Asin:               pgtype.Text{String: metadata.ASIN, Valid: metadata.ASIN != ""},
 		Description:        pgtype.Text{String: metadata.Description, Valid: metadata.Description != ""},
@@ -1018,8 +1024,9 @@ func (s *MediaScanner) processMediaFile(ctx context.Context, path string) (bool,
 		MimeType:           pgtype.Text{String: s.getMimeType(path), Valid: true},
 		CoverImagePath:     pgtype.Text{String: metadata.CoverPath, Valid: metadata.CoverPath != ""},
 		Series:             pgtype.Text{String: metadata.Series, Valid: metadata.Series != ""},
-		SeriesNumber:       pgtype.Int4{Int32: metadata.SeriesNumber, Valid: metadata.SeriesNumber > 0},
-		Publisher:          pgtype.Text{String: metadata.Publisher, Valid: metadata.Publisher != ""},
+		SeriesNumber:       pgtype.Float8{Float64: metadata.SeriesNumber, Valid: metadata.SeriesNumber > 0},
+		Publishers:         nilToEmpty(utils.SingleOrSlice(metadata.Publisher, metadata.Publishers)),
+		PublishersSearch:   utils.NormalizeTagsSearch(utils.SingleOrSlice(metadata.Publisher, metadata.Publishers)),
 		DatePublished:      pgtype.Date{Time: metadata.PublishDate, Valid: !metadata.PublishDate.IsZero()},
 		Genre:              pgtype.Text{String: metadata.Genre, Valid: metadata.Genre != ""},
 		Contributors:       metadata.Contributors,
@@ -1027,6 +1034,7 @@ func (s *MediaScanner) processMediaFile(ctx context.Context, path string) (bool,
 		Narrators:          nilToEmpty(metadata.Narrators),
 		NarratorsSearch:    utils.NormalizeNarratorsSearch(metadata.Narrators),
 		Abridged:           metadata.Abridged,
+		Explicit:           metadata.Explicit,
 		Tags:               metadata.Tags,
 		TagsSearch:         tagsSearch,
 		AddedByAdminID:     s.adminID,
@@ -1240,8 +1248,8 @@ func extractAudiobookshelfSidecar(path string) *MediaMetadata {
 	}
 	if seriesName != "" {
 		metadata.Series = strings.TrimSpace(seriesName)
-		if index, err := strconv.ParseFloat(strings.TrimSpace(seriesSequence), 32); err == nil {
-			metadata.SeriesNumber = int32(index)
+		if index, err := strconv.ParseFloat(strings.TrimSpace(seriesSequence), 64); err == nil {
+			metadata.SeriesNumber = index
 		}
 	}
 	if tags := append(append([]string{}, sidecar.Genres...), sidecar.Tags...); len(tags) > 0 {
@@ -1400,7 +1408,7 @@ func (s *MediaScanner) mergeMetadata(path string, calibreMetadata *MediaMetadata
 				metadata.Series = comicInfo.Series
 			}
 			if metadata.SeriesNumber == 0 && comicInfo.Number > 0 {
-				metadata.SeriesNumber = int32(comicInfo.Number)
+				metadata.SeriesNumber = float64(comicInfo.Number)
 			}
 			if metadata.Publisher == "" && comicInfo.Publisher != "" {
 				metadata.Publisher = comicInfo.Publisher
@@ -2221,7 +2229,7 @@ func parseOPFContent(content []byte) (*MediaMetadata, error) {
 	if series, index := opf.readSeries(); series != "" {
 		metadata.Series = series
 		if index > 0 {
-			metadata.SeriesNumber = int32(index)
+			metadata.SeriesNumber = index
 		}
 	}
 	// Calibre-specific meta tags (filter by name attribute)
@@ -3329,20 +3337,24 @@ func (s *MediaScanner) updateMediaItemWithMetadata(ctx context.Context, existing
 	params := database.UpdateMediaItemParams{
 		ID:                 existing.ID,
 		Title:              metadata.Title,
-		Author:             pgtype.Text{String: metadata.Author, Valid: metadata.Author != ""},
+		Subtitle:           pgtype.Text{String: metadata.Subtitle, Valid: metadata.Subtitle != ""},
+		Authors:            nilToEmpty(utils.SingleOrSlice(metadata.Author, metadata.Authors)),
+		AuthorsSearch:      utils.NormalizeTagsSearch(utils.SingleOrSlice(metadata.Author, metadata.Authors)),
 		Isbn:               pgtype.Text{String: utils.NormalizeISBNSafe(metadata.ISBN), Valid: metadata.ISBN != ""},
 		Description:        pgtype.Text{String: metadata.Description, Valid: metadata.Description != ""},
 		CoverImagePath:     pgtype.Text{String: s.getRelativePath(metadata.CoverPath), Valid: metadata.CoverPath != ""},
 		Series:             pgtype.Text{String: metadata.Series, Valid: metadata.Series != ""},
-		SeriesNumber:       pgtype.Int4{Int32: metadata.SeriesNumber, Valid: metadata.SeriesNumber > 0},
+		SeriesNumber:       pgtype.Float8{Float64: metadata.SeriesNumber, Valid: metadata.SeriesNumber > 0},
 		Narrators:          nilToEmpty(metadata.Narrators),
 		NarratorsSearch:    utils.NormalizeNarratorsSearch(metadata.Narrators),
 		Abridged:           metadata.Abridged,
+		Explicit:           metadata.Explicit,
 		Tags:               metadata.Tags,
 		TagsSearch:         tagsSearch,
 		Asin:               pgtype.Text{String: metadata.ASIN, Valid: metadata.ASIN != ""},
 		DatePublished:      pgtype.Date{Time: metadata.PublishDate, Valid: !metadata.PublishDate.IsZero()},
-		Publisher:          pgtype.Text{String: metadata.Publisher, Valid: metadata.Publisher != ""},
+		Publishers:         nilToEmpty(utils.SingleOrSlice(metadata.Publisher, metadata.Publishers)),
+		PublishersSearch:   utils.NormalizeTagsSearch(utils.SingleOrSlice(metadata.Publisher, metadata.Publishers)),
 		Contributors:       metadata.Contributors,
 		ContributorsSearch: contributorsSearch,
 		Language:           pgtype.Text{String: metadata.Language, Valid: metadata.Language != ""},