feat: manga metadata with status, authors, genres, tags, and search filters (0.15.0)

Adds first-class manga metadata across the stack:

- **Status** (ongoing / completed), **alternative titles**, normalized
  **multi-author** support, **curated genres** (13 seeded), and
  **free-form user tags** (case-insensitive, globally shared). Each is
  modelled as its own table joined to mangas; `mangas.author` is
  backfilled into `authors` + `manga_authors` and dropped.
- New endpoints: `PATCH /v1/mangas/:id` (three-state `description`),
  `POST/DELETE /v1/mangas/:id/tags[/:tag_id]`, `GET /v1/genres`,
  `GET /v1/tags?search=`.
- `GET /v1/mangas` now returns `MangaCard` (with authors + genres
  batched in) and supports `?status=`, `?author_id=`, `?genre_id=`,
  `?tag_id=` filters — AND across facets, with empty-array no-op
  semantics for the unnest primitive.
- `GET /v1/mangas/:id` returns the enriched `MangaDetail` with tags.
- Frontend: reusable `Chip` component; manga detail page renders
  authors as chips linking to `/authors/:id` (Phase 2), a status
  badge, alt titles, genres, and tags with inline add/remove (only
  the attacher sees remove); upload form supports multi-author /
  multi-genre / alt titles / status; search page gets a collapsible
  URL-synced filter panel with keyboard-navigable tag autocomplete.
- 126 backend tests (incl. AND-across-facets primitive, case-insens
  author/tag de-dup, transactional create rollback, PATCH semantics
  for missing / null / set on description); 72 frontend tests +
  svelte-check clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/migrations/0009_manga_metadata.sql

@@ -0,0 +1,102 @@
+-- Manga metadata: status, alternative titles, normalized authors,
+-- curated genres, and user-extensible tags. Each new concept gets its
+-- own table joined to mangas rather than being jammed onto the mangas
+-- row, in line with the extension philosophy in 0001_init.sql.
+
+-- 1. Inline columns: status (curated enum-like) and alt_titles (array).
+ALTER TABLE mangas
+    ADD COLUMN status text NOT NULL DEFAULT 'ongoing'
+        CHECK (status IN ('ongoing', 'completed')),
+    ADD COLUMN alt_titles text[] NOT NULL DEFAULT '{}';
+
+-- 2. Authors: normalized so an author page can list works.
+--    Display name preserves casing; lookups go through lower(name) for
+--    case-insensitive de-dup. Trigram index supports autocomplete.
+CREATE TABLE authors (
+    id          uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+    name        text NOT NULL,
+    created_at  timestamptz NOT NULL DEFAULT now()
+);
+CREATE UNIQUE INDEX authors_name_lower_uniq ON authors (lower(name));
+CREATE INDEX authors_name_trgm_idx ON authors USING gin (name gin_trgm_ops);
+
+CREATE TABLE manga_authors (
+    manga_id   uuid NOT NULL REFERENCES mangas(id) ON DELETE CASCADE,
+    author_id  uuid NOT NULL REFERENCES authors(id) ON DELETE CASCADE,
+    position   integer NOT NULL DEFAULT 0,
+    PRIMARY KEY (manga_id, author_id)
+);
+CREATE INDEX manga_authors_author_idx ON manga_authors (author_id);
+
+-- 3. Genres: curated controlled vocabulary, seeded below. Uploaders
+--    pick from this list; users do not add new genres (that's what
+--    tags are for).
+CREATE TABLE genres (
+    id    uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+    name  text NOT NULL UNIQUE
+);
+
+INSERT INTO genres (name) VALUES
+    ('Action'),
+    ('Adventure'),
+    ('Comedy'),
+    ('Drama'),
+    ('Fantasy'),
+    ('Horror'),
+    ('Mystery'),
+    ('Romance'),
+    ('Sci-Fi'),
+    ('Slice of Life'),
+    ('Sports'),
+    ('Supernatural'),
+    ('Thriller')
+ON CONFLICT DO NOTHING;
+
+CREATE TABLE manga_genres (
+    manga_id  uuid NOT NULL REFERENCES mangas(id) ON DELETE CASCADE,
+    genre_id  uuid NOT NULL REFERENCES genres(id) ON DELETE CASCADE,
+    PRIMARY KEY (manga_id, genre_id)
+);
+CREATE INDEX manga_genres_genre_idx ON manga_genres (genre_id);
+
+-- 4. Tags: free-form but globally shared. Any signed-in user can
+--    attach a tag to a manga — creating the tag if new. `added_by`
+--    records the attacher so the UI can show a remove button only to
+--    them. ON DELETE SET NULL keeps the tag intact if the user leaves.
+CREATE TABLE tags (
+    id          uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+    name        text NOT NULL,
+    created_at  timestamptz NOT NULL DEFAULT now()
+);
+CREATE UNIQUE INDEX tags_name_lower_uniq ON tags (lower(name));
+CREATE INDEX tags_name_trgm_idx ON tags USING gin (name gin_trgm_ops);
+
+CREATE TABLE manga_tags (
+    manga_id    uuid NOT NULL REFERENCES mangas(id) ON DELETE CASCADE,
+    tag_id      uuid NOT NULL REFERENCES tags(id) ON DELETE CASCADE,
+    added_by    uuid REFERENCES users(id) ON DELETE SET NULL,
+    created_at  timestamptz NOT NULL DEFAULT now(),
+    PRIMARY KEY (manga_id, tag_id)
+);
+CREATE INDEX manga_tags_tag_idx ON manga_tags (tag_id);
+
+-- 5. Backfill the existing single `author` column into the normalized
+--    tables. Trim whitespace; skip blanks. After backfill, drop the
+--    trigram index on the old column and then drop the column itself.
+INSERT INTO authors (name)
+    SELECT DISTINCT trim(author)
+      FROM mangas
+     WHERE author IS NOT NULL
+       AND trim(author) <> ''
+ON CONFLICT (lower(name)) DO NOTHING;
+
+INSERT INTO manga_authors (manga_id, author_id, position)
+    SELECT m.id, a.id, 0
+      FROM mangas m
+      JOIN authors a ON lower(a.name) = lower(trim(m.author))
+     WHERE m.author IS NOT NULL
+       AND trim(m.author) <> ''
+ON CONFLICT DO NOTHING;
+
+DROP INDEX IF EXISTS mangas_author_trgm_idx;
+ALTER TABLE mangas DROP COLUMN author;