feat(peer): remove downloaded game files safely

Downloaded but uninstalled games can still occupy significant disk space. Add a
separate removal path for that state instead of overloading uninstall, which is
reserved for deleting only `local/` installs.

The peer runtime now exposes `RemoveDownloadedGame` with matching lifecycle
and active-operation events. The filesystem delete is intentionally strict: the
id must be a catalog game and a single path component, the target must be a
direct child of the configured game directory, the root must not be a symlink,
it must have a regular root-level `version.ini`, and it must not contain
`local/`, `.local.installing/`, or `.local.backup/`. Only then do we recursively
remove the game root.

The Tauri bridge exposes this as `remove_downloaded_game`, the frontend shows a
matching danger action only for downloaded-but-uninstalled games, and a
confirmation dialog warns that re-downloading can take a long time.

Test Plan:
- git diff --check
- just fmt
- RUSTC_WRAPPER= CARGO_BUILD_RUSTC_WRAPPER= just test
- RUSTC_WRAPPER= CARGO_BUILD_RUSTC_WRAPPER= just clippy
- RUSTC_WRAPPER= CARGO_BUILD_RUSTC_WRAPPER= just build

Refs: user redesign nitpick about removing downloaded uninstalled games

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

@@ -8,13 +8,14 @@ export interface GameActions {
     install: (id: string) => Promise<void>;
     update: (id: string) => Promise<void>;
     uninstall: (id: string) => Promise<void>;
+    removeDownload: (id: string) => Promise<void>;
 }
 
 /**
  * Thin wrappers over the backend `run_game` / `install_game` / `update_game`
- * / `uninstall_game` commands. We mark peer-backed downloads as "checking
- * peers" and already-downloaded installs as "installing" up-front so the UI
- * doesn't have to wait for the first backend event.
+ * / `uninstall_game` / `remove_downloaded_game` commands. We mark peer-backed
+ * downloads as "checking peers" and already-downloaded installs as "installing"
+ * up-front so the UI doesn't have to wait for the first backend event.
  */
 export const useGameActions = (games: UseGamesResult): GameActions => {
     const play = useCallback(async (id: string) => {
@@ -58,5 +59,13 @@ export const useGameActions = (games: UseGamesResult): GameActions => {
         }
     }, []);
 
-    return { play, install, update, uninstall };
+    const removeDownload = useCallback(async (id: string) => {
+        try {
+            await invoke('remove_downloaded_game', { id });
+        } catch (err) {
+            console.error('remove_downloaded_game failed:', err);
+        }
+    }, []);
+
+    return { play, install, update, uninstall, removeDownload };
 };