feat(books): édition des métadonnées livres et séries + champ authors multi-valeurs

- Nouveaux endpoints PATCH /books/:id et PATCH /libraries/:id/series/:name pour éditer les métadonnées
- GET /libraries/:id/series/:name/metadata pour récupérer les métadonnées de série
- Ajout du champ `authors` (Vec<String>) sur les structs Book/BookDetails
- 3 migrations : table series_metadata, colonne authors sur series_metadata et books
- Composants EditBookForm et EditSeriesForm dans le backoffice
- Routes API Next.js correspondantes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

infra/migrations/0021_add_series_metadata.sql

@@ -0,0 +1,10 @@
+CREATE TABLE series_metadata (
+    library_id UUID    NOT NULL REFERENCES libraries(id) ON DELETE CASCADE,
+    name       TEXT    NOT NULL,
+    description TEXT,
+    publisher   TEXT,
+    start_year  INTEGER,
+    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    PRIMARY KEY (library_id, name)
+);

infra/migrations/0022_add_authors_to_series_metadata.sql

@@ -0,0 +1,8 @@
+ALTER TABLE series_metadata
+    ADD COLUMN authors    TEXT[] NOT NULL DEFAULT '{}',
+    ADD COLUMN publishers TEXT[] NOT NULL DEFAULT '{}';
+
+-- Migrate existing scalar publisher → publishers array
+UPDATE series_metadata SET publishers = ARRAY[publisher] WHERE publisher IS NOT NULL AND publisher != '';
+
+ALTER TABLE series_metadata DROP COLUMN publisher;

infra/migrations/0023_add_authors_to_books.sql

@@ -0,0 +1,5 @@
+ALTER TABLE books
+    ADD COLUMN authors TEXT[] NOT NULL DEFAULT '{}';
+
+-- Migrate existing scalar author → authors array
+UPDATE books SET authors = ARRAY[author] WHERE author IS NOT NULL AND author != '';