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/utils/metadata_overrides.go

@@ -18,7 +18,7 @@ import (
 
 const (
 	OverrideTitle            = "title"
-	OverrideAuthor           = "author"
+	OverrideAuthor           = "author" // protects the authors[] array (legacy key preserved)
 	OverrideISBN             = "isbn"
 	OverrideDescription      = "description"
 	OverrideCoverImagePath   = "cover_image_path"
@@ -29,7 +29,9 @@ const (
 	OverrideTags             = "tags"
 	OverrideAsin             = "asin"
 	OverrideDatePublished    = "date_published"
-	OverridePublisher        = "publisher"
+	OverrideSubtitle         = "subtitle"
+	OverrideExplicit         = "explicit"
+	OverridePublisher        = "publisher" // protects the publishers[] array (legacy key preserved)
 	OverrideContributors     = "contributors"
 	OverrideLanguage         = "language"
 	OverrideEdition          = "edition"
@@ -150,17 +152,19 @@ func detectMetadataOverridesDiff(params database.UpdateMediaItemParams, existing
 	}
 
 	add(OverrideTitle, params.Title != existing.Title)
-	add(OverrideAuthor, normText(params.Author) != normText(existing.Author))
+	add(OverrideSubtitle, normText(params.Subtitle) != normText(existing.Subtitle))
+	add(OverrideAuthor, normStringSlice(params.Authors) != normStringSlice(existing.Authors))
 	add(OverrideISBN, normText(params.Isbn) != normText(existing.Isbn))
 	add(OverrideDescription, normText(params.Description) != normText(existing.Description))
 	add(OverrideSeries, normText(params.Series) != normText(existing.Series))
-	add(OverrideSeriesNumber, normInt(params.SeriesNumber) != normInt(existing.SeriesNumber))
+	add(OverrideSeriesNumber, normFloat(params.SeriesNumber) != normFloat(existing.SeriesNumber))
 	add(OverrideTags, normStringSlice(params.Tags) != normStringSlice(existing.Tags))
 	add(OverrideNarrators, normStringSlice(params.Narrators) != normStringSlice(existing.Narrators))
 	add(OverrideAbridged, params.Abridged != existing.Abridged)
+	add(OverrideExplicit, params.Explicit != existing.Explicit)
 	add(OverrideAsin, normText(params.Asin) != normText(existing.Asin))
 	add(OverrideDatePublished, normDate(params.DatePublished) != normDate(existing.DatePublished))
-	add(OverridePublisher, normText(params.Publisher) != normText(existing.Publisher))
+	add(OverridePublisher, normStringSlice(params.Publishers) != normStringSlice(existing.Publishers))
 	add(OverrideContributors, normStringSlice(params.Contributors) != normStringSlice(existing.Contributors))
 	add(OverrideLanguage, normText(params.Language) != normText(existing.Language))
 	add(OverrideEdition, normText(params.Edition) != normText(existing.Edition))
@@ -205,8 +209,12 @@ func ApplyMetadataOverrides(params *database.UpdateMediaItemParams, existing dat
 	if hasOverride(o, OverrideTitle) {
 		params.Title = existing.Title
 	}
+	if hasOverride(o, OverrideSubtitle) {
+		params.Subtitle = existing.Subtitle
+	}
 	if hasOverride(o, OverrideAuthor) {
-		params.Author = existing.Author
+		params.Authors = existing.Authors
+		params.AuthorsSearch = existing.AuthorsSearch
 	}
 	if hasOverride(o, OverrideISBN) {
 		params.Isbn = existing.Isbn
@@ -241,7 +249,8 @@ func ApplyMetadataOverrides(params *database.UpdateMediaItemParams, existing dat
 		params.DatePublished = existing.DatePublished
 	}
 	if hasOverride(o, OverridePublisher) {
-		params.Publisher = existing.Publisher
+		params.Publishers = existing.Publishers
+		params.PublishersSearch = existing.PublishersSearch
 	}
 	if hasOverride(o, OverrideContributors) {
 		params.Contributors = existing.Contributors

internal/utils/metadata_overrides_test.go

@@ -63,12 +63,12 @@ func TestDetectMetadataOverridesUnsetFormsEqual(t *testing.T) {
 	// Zero-value params must not look "changed" against NULL-ish columns.
 	existing := database.MediaItems{
 		PageCount:       pgtype.Int4{Int32: 0, Valid: false},
-		SeriesNumber:    pgtype.Int4{Int32: 5, Valid: true},
+		SeriesNumber:    pgtype.Float8{Float64: 5, Valid: true},
 		CommunityRating: pgtype.Float8{Float64: 0, Valid: false},
 	}
 	params := database.UpdateMediaItemParams{
 		PageCount:       pgtype.Int4{Int32: 0, Valid: false},
-		SeriesNumber:    pgtype.Int4{Int32: 0, Valid: false}, // cleared by user -> changed
+		SeriesNumber:    pgtype.Float8{Float64: 0, Valid: false}, // cleared by user -> changed
 		CommunityRating: pgtype.Float8{Float64: 0, Valid: false},
 	}
 	got := DetectMetadataOverrides(params, existing)

internal/utils/tags.go

@@ -183,6 +183,21 @@ func NormalizeNarratorsSearch(narrators []string) []string {
 	return NormalizeTagsSearch(narrators)
 }
 
+// SingleOrSlice returns the write-truth array for a field that has both a
+// legacy single-value form and an array form: the explicit array when
+// populated, else the single string as a one-element slice. Used by the
+// authors/publishers arrays (`author`/`publisher` varchars regenerate from
+// them via the sync_author_publisher_display trigger).
+func SingleOrSlice(single string, arr []string) []string {
+	if len(arr) > 0 {
+		return arr
+	}
+	if single == "" {
+		return []string{}
+	}
+	return []string{single}
+}
+
 // NormalizeContributors normalizes an array of contributors for display:
 // 1. Trim whitespace
 // 2. Preserve original casing (including CAPSLOCK companies)