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).

database/schema/schema.sql

@@ -136,7 +136,8 @@ CREATE TABLE IF NOT EXISTS media_items (
     id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
     library_id UUID NOT NULL REFERENCES libraries(id) ON DELETE CASCADE,
     title VARCHAR(255) NOT NULL,
-    author VARCHAR(255),
+    subtitle TEXT, -- Series-y/edition subtitle from sidecars; display field, never part of `title`
+    author VARCHAR(255), -- DEPRECATED for writes: display string regenerated from `authors` by trigger
     isbn VARCHAR(13), -- Still relevant for ebooks
     description TEXT,
     file_path VARCHAR(500) NOT NULL,
@@ -144,10 +145,15 @@ CREATE TABLE IF NOT EXISTS media_items (
     mime_type VARCHAR(100),
     cover_image_path VARCHAR(500),
     series VARCHAR(255),
-    series_number INTEGER,
+    series_number DOUBLE PRECISION, -- Real ordinals are decimals (0.5, 1.5 novellas); was INTEGER
     tags TEXT[],
     narrators TEXT[], -- Audiobook narrators (sidecar first; user-editable)
+    authors TEXT[] NOT NULL DEFAULT '{}', -- Write truth for authorship; `author` above is trigger-regenerated display
+    authors_search TEXT[] NOT NULL DEFAULT '{}',
+    publishers TEXT[] NOT NULL DEFAULT '{}', -- Write truth; `publisher` below is trigger-regenerated display
+    publishers_search TEXT[] NOT NULL DEFAULT '{}',
     abridged BOOLEAN NOT NULL DEFAULT FALSE, -- Libation/Audible abridged flag
+    explicit BOOLEAN NOT NULL DEFAULT FALSE, -- Adult flag from sidecars (ABS explicit / Audible isAdult)
     asin VARCHAR(20), -- Still relevant for ebooks
     date_published DATE,
     publisher VARCHAR(255),
@@ -267,6 +273,30 @@ ALTER TABLE media_items ADD COLUMN IF NOT EXISTS contributors_search TEXT[];
 ALTER TABLE media_items ADD COLUMN IF NOT EXISTS narrators TEXT[] NOT NULL DEFAULT '{}';
 ALTER TABLE media_items ADD COLUMN IF NOT EXISTS narrators_search TEXT[] NOT NULL DEFAULT '{}';
 ALTER TABLE media_items ADD COLUMN IF NOT EXISTS abridged BOOLEAN NOT NULL DEFAULT FALSE;
+
+-- A2b: subtitle + explicit flags, authors/publishers arrays (narrators
+-- precedent — arrays are write truth, varchar display columns regenerate).
+ALTER TABLE media_items ADD COLUMN IF NOT EXISTS subtitle TEXT;
+ALTER TABLE media_items ADD COLUMN IF NOT EXISTS explicit BOOLEAN NOT NULL DEFAULT FALSE;
+ALTER TABLE media_items ADD COLUMN IF NOT EXISTS authors TEXT[] NOT NULL DEFAULT '{}';
+ALTER TABLE media_items ADD COLUMN IF NOT EXISTS authors_search TEXT[] NOT NULL DEFAULT '{}';
+ALTER TABLE media_items ADD COLUMN IF NOT EXISTS publishers TEXT[] NOT NULL DEFAULT '{}';
+ALTER TABLE media_items ADD COLUMN IF NOT EXISTS publishers_search TEXT[] NOT NULL DEFAULT '{}';
+
+-- Series ordinals are real-world decimals (0.5, 1.5 novellas); INTEGER
+-- truncated them to the wrong shelf order. In-place widening; no-op on a
+-- fresh install (column is already double precision from CREATE TABLE).
+ALTER TABLE media_items ALTER COLUMN series_number TYPE double precision
+  USING series_number::double precision;
+
+-- Backfill the arrays from the legacy single-value columns. Deliberately NO
+-- comma-splitting ("Tolkien, J.R.R." would corrupt); every existing row is
+-- effectively single-valued because the scanner historically kept only
+-- authors[0]. Guarded so the pass is free after the first startup.
+UPDATE media_items SET authors = ARRAY[author]
+ WHERE author IS NOT NULL AND author <> '' AND authors = '{}';
+UPDATE media_items SET publishers = ARRAY[publisher]
+ WHERE publisher IS NOT NULL AND publisher <> '' AND publishers = '{}';
 -- audio_metadata is declared in the CREATE TABLE above, which only fresh
 -- installs ever see — this ALTER is the upgrade path for pre-A2 installs
 -- (its absence 42703'd every scan and archive pass on upgraded deployments).
@@ -316,6 +346,20 @@ BEGIN
   IF NEW.narrators_search IS NULL THEN
     NEW.narrators_search := '{}';
   END IF;
+  -- A2b: authors/publishers arrays are NOT NULL — Go nil slices become
+  -- explicit NULLs in params and would 23502 (the narrators lesson).
+  IF NEW.authors IS NULL THEN
+    NEW.authors := '{}';
+  END IF;
+  IF NEW.authors_search IS NULL THEN
+    NEW.authors_search := '{}';
+  END IF;
+  IF NEW.publishers IS NULL THEN
+    NEW.publishers := '{}';
+  END IF;
+  IF NEW.publishers_search IS NULL THEN
+    NEW.publishers_search := '{}';
+  END IF;
   RETURN NEW;
 END;
 $$ LANGUAGE plpgsql;
@@ -333,6 +377,35 @@ CREATE TRIGGER set_library_type_name_on_library_change
   FOR EACH ROW
   EXECUTE FUNCTION set_library_type_name();
 
+-- Display sync: `author`/`publisher` are denormalized display strings
+-- regenerated from the authors/publishers arrays on every write. The varchar
+-- columns face search (trgm), facets and API responses; the arrays are the
+-- write truth. array_to_string is STABLE on PG15 (not IMMUTABLE), so this
+-- must be a trigger — a generated column would reject it. Absent arrays
+-- yield NULL display (matches the legacy no-author row shape).
+DROP TRIGGER IF EXISTS sync_author_publisher_display_trg ON media_items;
+DROP FUNCTION IF EXISTS sync_author_publisher_display();
+CREATE OR REPLACE FUNCTION sync_author_publisher_display() RETURNS TRIGGER AS $$
+BEGIN
+  -- Defense in depth: normalize NULL arrays first (this trigger may fire
+  -- before set_library_type_name depending on name-ordered execution).
+  IF NEW.authors IS NULL THEN
+    NEW.authors := '{}';
+  END IF;
+  IF NEW.publishers IS NULL THEN
+    NEW.publishers := '{}';
+  END IF;
+  NEW.author    := CASE WHEN NEW.authors    = '{}' THEN NULL
+                        ELSE array_to_string(NEW.authors, ', ') END;
+  NEW.publisher := CASE WHEN NEW.publishers = '{}' THEN NULL
+                        ELSE array_to_string(NEW.publishers, ', ') END;
+  RETURN NEW;
+END $$ LANGUAGE plpgsql;
+CREATE TRIGGER sync_author_publisher_display_trg
+  BEFORE INSERT OR UPDATE ON media_items
+  FOR EACH ROW
+  EXECUTE FUNCTION sync_author_publisher_display();
+
 -- Add GIN indexes for pg_trgm fuzzy search performance
 CREATE INDEX IF NOT EXISTS idx_media_items_author_trgm
   ON media_items USING GIN (author gin_trgm_ops);
@@ -1256,12 +1329,21 @@ CREATE TABLE IF NOT EXISTS collection_items (
     added_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
     added_by_user_id UUID REFERENCES users(id) ON DELETE SET NULL,
     excluded BOOLEAN DEFAULT false,
+    -- Manual playlist ordering (reading-order collections). NULL = un-ordered
+    -- legacy item; ordering falls back to added_at ASC.
+    position INTEGER,
     UNIQUE(collection_id, media_item_id)
 );
 
 CREATE INDEX IF NOT EXISTS idx_collection_items_collection ON collection_items(collection_id);
 CREATE INDEX IF NOT EXISTS idx_collection_items_media ON collection_items(media_item_id);
 
+-- Playlist ordering (A2c): position-first ordering for collection listings;
+-- NULLs fall back to added_at ASC.
+ALTER TABLE collection_items ADD COLUMN IF NOT EXISTS position INTEGER;
+CREATE INDEX IF NOT EXISTS idx_collection_items_order
+  ON collection_items(collection_id, position ASC NULLS LAST);
+
 -- Index for excluding auto-assigned items
 CREATE INDEX IF NOT EXISTS idx_collection_items_excluded ON collection_items(collection_id, excluded)
     WHERE excluded = true;