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/download_detection.rs

@@ -441,7 +441,7 @@ pub async fn delete_available_download(
     State(state): State<AppState>,
     Path(id): Path<Uuid>,
     axum::extract::Query(query): axum::extract::Query<DeleteAvailableQuery>,
-) -> Result<Json<serde_json::Value>, ApiError> {
+) -> Result<Json<crate::responses::OkResponse>, ApiError> {
     if let Some(release_idx) = query.release {
         // Remove a single release from the JSON array
         let row = sqlx::query("SELECT available_releases FROM available_downloads WHERE id = $1")
@@ -486,7 +486,7 @@ pub async fn delete_available_download(
         }
     }
 
-    Ok(Json(serde_json::json!({ "ok": true })))
+    Ok(Json(crate::responses::OkResponse::new()))
 }
 
 #[derive(Deserialize)]