feat(ui): move game folder picker into settings

The design update moved game-folder configuration out of launcher chrome and
into Settings > Library. Follow that contract in the runtime UI without
changing the existing storage or Tauri directory commands.

The top bar now leaves its right edge for the kebab menu. Settings owns a new
Game folder row that shows a valid selected path with a neutral Change button,
or the red Not set state with a stronger Choose button when no accessible
directory is configured. Both the empty-library state and the Settings row
still use the existing native directory picker, so existing saved paths and
rescans keep their current behavior.

Keep useGameDirectory as the directory-state owner and expose the shared
hasGameDirectory boolean from that hook so the grid and Settings field agree on
what counts as configured.

Test Plan:
- git diff --cached --check
- just frontend-test
- just build

Refs: 62b409f4bfc4995c25461776107d28f52b24f30e

crates/lanspread-tauri-deno-ts/src/hooks/useGameDirectory.ts

@@ -64,6 +64,8 @@ export const useGameDirectory = () => {
         };
     }, [gameDir]);
 
+    const hasGameDirectory = gameDir.trim() !== '' && gameDirExists;
+
     const rescan = useCallback(() => {
         if (!gameDir.trim()) {
             setGameDirExists(false);
@@ -86,5 +88,5 @@ export const useGameDirectory = () => {
         void sync();
     }, [gameDir]);
 
-    return { gameDir, gameDirExists, setGameDir, rescan };
+    return { gameDir, gameDirExists, hasGameDirectory, setGameDir, rescan };
 };