refactor(api): extract 8 content domains into api/*.ts slices (R7.5 S1)

Move feed, channels, sync, playlists, tags, notifications, saved-views and
quota out of the lib/api.ts god object into per-domain slice modules, each
owning its own types + method slice and spread into the façade. The `api`
object shape and all 54 call sites are unchanged; account/auth/setup/admin
stay inline until S2.

Reunites the interleaved tags read/CRUD that motivated the epic.

frontend/src/lib/api/savedViews.ts

@@ -0,0 +1,28 @@
+// Saved "smart views": per-user named snapshots of FeedFilters (see SavedViewsWidget).
+// Only touches core's req; the FeedFilters shape is owned by feed.ts.
+import { req } from "./core";
+import type { FeedFilters } from "./feed";
+
+// A saved "smart view": a per-user named snapshot of FeedFilters (see SavedViewsWidget).
+export interface SavedView {
+  id: number;
+  name: string;
+  filters: FeedFilters;
+  position: number;
+  is_default: boolean;
+}
+
+export const savedViewsApi = {
+  savedViews: (): Promise<SavedView[]> => req("/api/saved-views"),
+  createView: (name: string, filters: FeedFilters): Promise<SavedView> =>
+    req("/api/saved-views", { method: "POST", body: JSON.stringify({ name, filters }) }),
+  updateView: (
+    id: number,
+    patch: Partial<{ name: string; filters: FeedFilters; is_default: boolean }>,
+  ): Promise<SavedView> =>
+    req(`/api/saved-views/${id}`, { method: "PATCH", body: JSON.stringify(patch) }),
+  deleteView: (id: number): Promise<{ deleted: number }> =>
+    req(`/api/saved-views/${id}`, { method: "DELETE" }),
+  reorderViews: (ids: number[]): Promise<{ ok: boolean }> =>
+    req("/api/saved-views/reorder", { method: "POST", body: JSON.stringify({ ids }) }),
+};