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/src/repo/genre.rs

@@ -0,0 +1,88 @@
+use std::collections::BTreeMap;
+
+use sqlx::{PgConnection, PgPool};
+use uuid::Uuid;
+
+use crate::domain::genre::{Genre, GenreRef};
+use crate::error::AppResult;
+
+pub async fn list_all(pool: &PgPool) -> AppResult<Vec<Genre>> {
+    let rows = sqlx::query_as::<_, Genre>(
+        "SELECT id, name FROM genres ORDER BY lower(name)",
+    )
+    .fetch_all(pool)
+    .await?;
+    Ok(rows)
+}
+
+pub async fn list_for_manga(pool: &PgPool, manga_id: Uuid) -> AppResult<Vec<GenreRef>> {
+    let rows = sqlx::query_as::<_, GenreRef>(
+        r#"
+        SELECT g.id, g.name
+          FROM manga_genres mg
+          JOIN genres g ON g.id = mg.genre_id
+         WHERE mg.manga_id = $1
+         ORDER BY lower(g.name)
+        "#,
+    )
+    .bind(manga_id)
+    .fetch_all(pool)
+    .await?;
+    Ok(rows)
+}
+
+pub async fn load_for_mangas(
+    pool: &PgPool,
+    manga_ids: &[Uuid],
+) -> AppResult<BTreeMap<Uuid, Vec<GenreRef>>> {
+    if manga_ids.is_empty() {
+        return Ok(BTreeMap::new());
+    }
+    let rows: Vec<(Uuid, Uuid, String)> = sqlx::query_as(
+        r#"
+        SELECT mg.manga_id, g.id, g.name
+          FROM manga_genres mg
+          JOIN genres g ON g.id = mg.genre_id
+         WHERE mg.manga_id = ANY($1)
+         ORDER BY mg.manga_id, lower(g.name)
+        "#,
+    )
+    .bind(manga_ids)
+    .fetch_all(pool)
+    .await?;
+    let mut grouped: BTreeMap<Uuid, Vec<GenreRef>> = BTreeMap::new();
+    for (manga_id, id, name) in rows {
+        grouped.entry(manga_id).or_default().push(GenreRef { id, name });
+    }
+    Ok(grouped)
+}
+
+/// Replace the manga's genres. Unknown ids are silently ignored: the
+/// FK constraint would reject them, so we filter upstream rather than
+/// surface a 500 here. (The API layer validates the set against
+/// `list_all` first.)
+pub async fn set_for_manga(
+    conn: &mut PgConnection,
+    manga_id: Uuid,
+    genre_ids: &[Uuid],
+) -> AppResult<()> {
+    sqlx::query("DELETE FROM manga_genres WHERE manga_id = $1")
+        .bind(manga_id)
+        .execute(&mut *conn)
+        .await?;
+    if genre_ids.is_empty() {
+        return Ok(());
+    }
+    sqlx::query(
+        r#"
+        INSERT INTO manga_genres (manga_id, genre_id)
+        SELECT $1, unnest($2::uuid[])
+        ON CONFLICT DO NOTHING
+        "#,
+    )
+    .bind(manga_id)
+    .bind(genre_ids)
+    .execute(&mut *conn)
+    .await?;
+    Ok(())
+}