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.

frontend/src/features/online/OnlineDetail.tsx

@@ -16,6 +16,7 @@ import { DetailShell } from "@/features/detail/DetailShell";
 import { api, errorMessage } from "@/lib/api";
 import { cn } from "@/lib/cn";
 import { renderDText } from "@/lib/dtext";
+import { isTypingTarget } from "@/lib/dom";
 import {
   e621ErrorMessage,
   effectiveCredentials,
@@ -118,6 +119,19 @@ export function OnlineDetail({ postId }: { postId: number }) {
 
   const [downloadTaskId, setDownloadTaskId] = useState<string | null>(null);
 
+  useEffect(() => {
+    function handleKeyDown(event: KeyboardEvent) {
+      if (event.ctrlKey || event.metaKey || event.altKey) return;
+      if (isTypingTarget(event.target)) return;
+      if (event.key.toLowerCase() !== "f") return;
+      if (!post || !credentials?.configured || favoriteMutation.isPending) return;
+      event.preventDefault();
+      favoriteMutation.mutate(!post.is_favorited);
+    }
+    window.addEventListener("keydown", handleKeyDown);
+    return () => window.removeEventListener("keydown", handleKeyDown);
+  }, [post, credentials, favoriteMutation]);
+
   const downloadMutation = useMutation({
     mutationFn: (target: NonNullable<typeof post>) =>
       api<DownloadTask>("/api/online/downloads/", {
@@ -234,7 +248,7 @@ export function OnlineDetail({ postId }: { postId: number }) {
               onClick={() => favoriteMutation.mutate(!post.is_favorited)}
               title={
                 credentials?.configured
-                  ? undefined
+                  ? "Toggle favorite (F)"
                   : "Add e621 credentials in Account to favorite posts"
               }
             >