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/src/lib.rs

@@ -67,6 +67,7 @@ use crate::{
         handle_get_peer_count_command,
         handle_install_game_command,
         handle_list_games_command,
+        handle_remove_downloaded_game_command,
         handle_set_game_dir_command,
         handle_uninstall_game_command,
         load_local_library,
@@ -120,6 +121,12 @@ pub enum PeerEvent {
     UninstallGameFinished { id: String },
     /// Uninstall transaction has failed after rollback.
     UninstallGameFailed { id: String },
+    /// Downloaded archive removal has started for an uninstalled game.
+    RemoveDownloadedGameBegin { id: String },
+    /// Downloaded archive removal has completed successfully.
+    RemoveDownloadedGameFinished { id: String },
+    /// Downloaded archive removal has failed before deleting the game root.
+    RemoveDownloadedGameFailed { id: String },
     /// No peers have the requested game.
     NoPeersHaveGame { id: String },
     /// A peer has connected.
@@ -187,6 +194,8 @@ pub enum ActiveOperationKind {
     Updating,
     /// Removing an existing `local/` install.
     Uninstalling,
+    /// Removing downloaded archive files for an uninstalled game.
+    RemovingDownload,
 }
 
 /// Commands sent to the peer system from the UI.
@@ -213,6 +222,8 @@ pub enum PeerCommand {
     InstallGame { id: String },
     /// Remove only the `local/` install for a game.
     UninstallGame { id: String },
+    /// Remove downloaded archive files for an uninstalled game.
+    RemoveDownloadedGame { id: String },
     /// Set the local game directory.
     SetGameDir(PathBuf),
     /// Request the current peer count.
@@ -394,6 +405,9 @@ async fn handle_peer_commands(
             PeerCommand::UninstallGame { id } => {
                 handle_uninstall_game_command(ctx, tx_notify_ui, id).await;
             }
+            PeerCommand::RemoveDownloadedGame { id } => {
+                handle_remove_downloaded_game_command(ctx, tx_notify_ui, id).await;
+            }
             PeerCommand::SetGameDir(game_dir) => {
                 handle_set_game_dir_command(ctx, tx_notify_ui, game_dir).await;
             }