Add the F favorite shortcut and the Ctrl+K tag finder

The command palette now searches e621 tags as you type (debounced
/tags.json suggestions with category chips and post counts), lets you
search a tag online, follow/unfollow it inline and open it on e621, and
remembers recent searches in localStorage. New navigation commands cover
Pools, Followed and Similar. On the online detail, F toggles the current
post's favorite.

ROADMAP.md

@@ -69,7 +69,9 @@ they land.
         blacklist-aware) and deleted-pool markers
   - [x] Pool detail: DText description, posts kept in pool order with chunked
         loading and in-library badges, blacklist reveal toggle, Follow button
-- [ ] `F` shortcut to favorite a post, tag finder in the Ctrl+K palette
+- [x] `F` shortcut to favorite a post (online detail), tag finder in the Ctrl+K
+      palette (e621 tag suggestions with follow toggles, recent searches, and
+      "search e621 for …")
 
 ## 3. Uploads & ingestion pipeline
 
@@ -116,7 +118,8 @@ Files now stage first and are resolved before entering the library.
 - [x] Profile pictures: staff Users page sets avatars from library J-IDs
       (self-service picker in Account still pending)
 - [ ] Profile extras (per-user browse preferences)
-- [ ] Command palette: tag finder, recent searches
+- [x] Command palette: tag finder, recent searches, navigation commands
+      (Ctrl+K / ⌘K, reachable from anywhere in the shell)
 
 ## 6. Infrastructure