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_mangas.rs

@@ -158,7 +158,11 @@ async fn create_then_list_roundtrip(pool: PgPool) {
             "/api/v1/mangas",
             MultipartBuilder::new().add_json(
                 "metadata",
-                json!({ "title": "Berserk", "author": "Kentaro Miura", "description": null }),
+                json!({
+                    "title": "Berserk",
+                    "authors": ["Kentaro Miura"],
+                    "description": null,
+                }),
             ),
             &cookie,
         ))
@@ -167,14 +171,23 @@ async fn create_then_list_roundtrip(pool: PgPool) {
     assert_eq!(created.status(), StatusCode::CREATED);
     let body = common::body_json(created).await;
     assert_eq!(body["title"], "Berserk");
-    assert_eq!(body["author"], "Kentaro Miura");
+    let authors = body["authors"].as_array().unwrap();
+    assert_eq!(authors.len(), 1);
+    assert_eq!(authors[0]["name"], "Kentaro Miura");
     assert!(body["id"].as_str().is_some());
+    // Status defaults to ongoing; tags and genres start empty.
+    assert_eq!(body["status"], "ongoing");
+    assert_eq!(body["genres"], json!([]));
+    assert_eq!(body["tags"], json!([]));
 
     let listed = h.app.oneshot(common::get("/api/v1/mangas")).await.unwrap();
     let listed_body = common::body_json(listed).await;
     let items = listed_body["items"].as_array().unwrap();
     assert_eq!(items.len(), 1);
     assert_eq!(items[0]["title"], "Berserk");
+    // List endpoint returns the card shape: authors + genres included.
+    let authors = items[0]["authors"].as_array().unwrap();
+    assert_eq!(authors[0]["name"], "Kentaro Miura");
 }
 
 #[sqlx::test(migrations = "./migrations")]
@@ -193,13 +206,15 @@ async fn search_filters_by_title_and_author(pool: PgPool) {
             .oneshot(common::post_multipart_with_cookie(
                 "/api/v1/mangas",
                 MultipartBuilder::new()
-                    .add_json("metadata", json!({ "title": title, "author": author })),
+                    .add_json("metadata", json!({ "title": title, "authors": [author] })),
                 &cookie,
             ))
             .await
             .unwrap();
     }
 
+    // Searching by author name still works — the list query joins
+    // authors so 'miura' resolves through the manga_authors table.
     let resp = h
         .app
         .clone()