refactor: Phase E — types de réponses API standardisés + SVGs inline → Icon

E1 - API responses:
- Crée responses.rs avec OkResponse, DeletedResponse, UpdatedResponse,
  RevokedResponse, UnlinkedResponse, StatusResponse (6 tests de sérialisation)
- Remplace ~15 json!() inline par des types structurés dans books, libraries,
  tokens, users, handlers, anilist, metadata, download_detection, torrent_import
- Signatures de retour des handlers typées (plus de serde_json::Value)

E2 - SVGs → Icon component:
- Ajoute icon "lock" au composant Icon
- Remplace ~30 SVGs inline par <Icon> dans 9 composants
  (FolderPicker, FolderBrowser, LiveSearchForm, JobRow, LibraryActions,
  ReadingStatusModal, EditBookForm, EditSeriesForm, UserSwitcher)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/api/src/books.rs

@@ -669,7 +669,7 @@ pub async fn get_thumbnail(
 pub async fn delete_book(
     State(state): State<AppState>,
     Path(id): Path<Uuid>,
-) -> Result<Json<serde_json::Value>, ApiError> {
+) -> Result<Json<crate::responses::OkResponse>, ApiError> {
     // Fetch the book and its file path
     let row = sqlx::query(
         "SELECT b.library_id, b.thumbnail_path, bf.abs_path \
@@ -727,5 +727,5 @@ pub async fn delete_book(
         id, scan_job_id, library_id
     );
 
-    Ok(Json(serde_json::json!({ "ok": true })))
+    Ok(Json(crate::responses::OkResponse::new()))
 }