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/tests/api_genres.rs

@@ -0,0 +1,35 @@
+mod common;
+
+use axum::http::StatusCode;
+use sqlx::PgPool;
+use tower::ServiceExt;
+
+#[sqlx::test(migrations = "./migrations")]
+async fn lists_seeded_genres(pool: PgPool) {
+    let h = common::harness(pool);
+    let resp = h
+        .app
+        .oneshot(common::get("/api/v1/genres"))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::OK);
+    let body = common::body_json(resp).await;
+    let items = body.as_array().expect("genres returned as a flat array");
+    let names: Vec<&str> = items
+        .iter()
+        .map(|g| g["name"].as_str().unwrap())
+        .collect();
+    // The migration seeds a curated vocabulary; spot-check a few
+    // common ones so accidental removals fail loudly.
+    for expected in ["Action", "Comedy", "Romance", "Sci-Fi"] {
+        assert!(
+            names.contains(&expected),
+            "expected seeded genre {expected:?} in {names:?}"
+        );
+    }
+    // Every genre must carry an id so the create/patch endpoints have
+    // something to reference.
+    for g in items {
+        assert!(g["id"].as_str().is_some());
+    }
+}