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-peer-cli/src/main.rs

@@ -460,31 +460,24 @@ async fn update_state_from_event(shared: &SharedState, event: PeerEvent) -> (&'s
                 "length": length,
             }),
         ),
-        PeerEvent::DownloadGameFilesFinished { id } => {
-            ("download-finished", json!({"game_id": id}))
-        }
-        PeerEvent::DownloadGameFilesFailed { id } => ("download-failed", json!({"game_id": id})),
-        PeerEvent::DownloadGameFilesAllPeersGone { id } => {
-            ("download-peers-gone", json!({"game_id": id}))
-        }
+        PeerEvent::DownloadGameFilesFinished { id } => game_id_event("download-finished", id),
+        PeerEvent::DownloadGameFilesFailed { id } => game_id_event("download-failed", id),
+        PeerEvent::DownloadGameFilesAllPeersGone { id } => game_id_event("download-peers-gone", id),
         PeerEvent::InstallGameBegin { id, operation } => (
             "install-begin",
             json!({"game_id": id, "operation": install_operation_name(operation)}),
         ),
-        PeerEvent::InstallGameFinished { id } => ("install-finished", json!({"game_id": id})),
-        PeerEvent::InstallGameFailed { id } => ("install-failed", json!({"game_id": id})),
-        PeerEvent::UninstallGameBegin { id } => ("uninstall-begin", json!({"game_id": id})),
-        PeerEvent::UninstallGameFinished { id } => ("uninstall-finished", json!({"game_id": id})),
-        PeerEvent::UninstallGameFailed { id } => ("uninstall-failed", json!({"game_id": id})),
-        PeerEvent::NoPeersHaveGame { id } => {
-            shared
-                .state
-                .write()
-                .await
-                .unavailable_games
-                .insert(id.clone());
-            ("no-peers-have-game", json!({"game_id": id}))
+        PeerEvent::InstallGameFinished { id } => game_id_event("install-finished", id),
+        PeerEvent::InstallGameFailed { id } => game_id_event("install-failed", id),
+        PeerEvent::UninstallGameBegin { id } => game_id_event("uninstall-begin", id),
+        PeerEvent::UninstallGameFinished { id } => game_id_event("uninstall-finished", id),
+        PeerEvent::UninstallGameFailed { id } => game_id_event("uninstall-failed", id),
+        PeerEvent::RemoveDownloadedGameBegin { id } => game_id_event("remove-download-begin", id),
+        PeerEvent::RemoveDownloadedGameFinished { id } => {
+            game_id_event("remove-download-finished", id)
         }
+        PeerEvent::RemoveDownloadedGameFailed { id } => game_id_event("remove-download-failed", id),
+        PeerEvent::NoPeersHaveGame { id } => no_peers_event(shared, id).await,
         PeerEvent::PeerConnected(addr) => ("peer-connected", peer_addr_json(addr)),
         PeerEvent::PeerDisconnected(addr) => ("peer-disconnected", peer_addr_json(addr)),
         PeerEvent::PeerDiscovered(addr) => ("peer-discovered", peer_addr_json(addr)),
@@ -497,6 +490,20 @@ async fn update_state_from_event(shared: &SharedState, event: PeerEvent) -> (&'s
     }
 }
 
+fn game_id_event(kind: &'static str, id: String) -> (&'static str, Value) {
+    (kind, json!({"game_id": id}))
+}
+
+async fn no_peers_event(shared: &SharedState, id: String) -> (&'static str, Value) {
+    shared
+        .state
+        .write()
+        .await
+        .unavailable_games
+        .insert(id.clone());
+    game_id_event("no-peers-have-game", id)
+}
+
 fn peer_addr_json(addr: SocketAddr) -> Value {
     json!({"addr": addr.to_string()})
 }