Follows: followed tags/pools, feeds, unseen badges and blacklist cloud

Backend (new apps.follows):
- FollowedTag/FollowedPool/FollowedPost models; per-user follows with
  unseen tracking, plus FollowCloud for the cached blacklist cloud.
- Two periodic commands sharing one fetch path: sync_followed_tags and
  sync_followed_pools fetch each followed tag/pool's newest posts (one
  e621 search per unique follow), store unseen feed rows, refresh covers
  and pool metadata; both fall back to anonymous e621 access.
- API: /api/follows/tags|pools (follow, unfollow, mark seen), a merged
  feed with per-follow filtering, and /api/follows/cloud/ which rebuilds
  the blacklisted-tag cloud in a daemon thread when its 10 min cache is
  stale (polling returns building/ready).
- e621 client now supports anonymous reads; trimmed posts carry preview
  URLs for covers and feed tiles.

Frontend:
- /followed page: follow forms, cover cards with unseen badges and
  Mark seen, merged feed with filter/unseen toggle, and a blacklist
  cloud panel that polls while building. Followed nav entry added.

frontend/src/lib/types.ts

@@ -204,6 +204,77 @@ export interface MatchTask {
   updated_at: string;
 }
 
+export interface FollowCoverData {
+  post_id: number | null;
+  rating: string | null;
+  preview_url: string | null;
+  score: number | null;
+  fav_count: number | null;
+}
+
+export interface FollowedTag {
+  id: number;
+  tag: string;
+  unseen_count: number;
+  cover_data: FollowCoverData | null;
+  last_synced_at: string | null;
+  created_at: string;
+}
+
+export interface FollowedPool {
+  id: number;
+  pool_id: number;
+  name: string;
+  post_count: number;
+  unseen_count: number;
+  cover_data: FollowCoverData | null;
+  last_synced_at: string | null;
+  created_at: string;
+}
+
+export interface FollowFeedSource {
+  kind: "tag" | "pool";
+  id: number;
+  label: string;
+}
+
+export interface FollowFeedEntry {
+  post_id: number;
+  seen: boolean;
+  data: {
+    id?: number | null;
+    rating?: string | null;
+    tags?: Record<string, string[]>;
+    score?: { total?: number | null } | null;
+    fav_count?: number | null;
+    file?: {
+      width?: number | null;
+      height?: number | null;
+      ext?: string | null;
+    } | null;
+    preview?: { url?: string | null } | null;
+  };
+  sources: FollowFeedSource[];
+}
+
+export interface FollowFeed {
+  count: number;
+  page: number;
+  per_page: number;
+  has_next: boolean;
+  results: FollowFeedEntry[];
+}
+
+export interface FollowCloud {
+  status: "ready" | "building";
+  stale: boolean;
+  tags: [string, number][];
+  posts: number;
+  source: "user" | "default" | null;
+  blacklist_count: number;
+  computed_at: string | null;
+}
+
 export interface E621IqdbCandidate {
   post_id: number | null;
   score: number | null;