feat(ui): add download progress controls

Replace the downloading action button with a dedicated progress component in
both card and detail views. The card now shows percent plus current speed, while
the detail modal shows bytes, speed, ETA, percent, and an inline cancel affordance
using the same backend progress payload.

Expose download cancellation as a peer command that cancels the tracked transfer
token and lets the running operation clear the authoritative active-operation
snapshot. Add a View Files action that resolves the game root safely and opens it
with the platform file viewer through Tauri's shell plugin.

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

Refs: design reference e308009a08

crates/lanspread-peer/src/lib.rs

@@ -61,6 +61,7 @@ use crate::{
     context::Ctx,
     handlers::{
         GameDetailSource,
+        handle_cancel_download_command,
         handle_connect_peer_command,
         handle_download_game_files_command,
         handle_get_game_command,
@@ -235,6 +236,8 @@ pub enum PeerCommand {
     UninstallGame { id: String },
     /// Remove downloaded archive files for an uninstalled game.
     RemoveDownloadedGame { id: String },
+    /// Cancel an active peer download without emitting a user-facing failure.
+    CancelDownload { id: String },
     /// Set the local game directory.
     SetGameDir(PathBuf),
     /// Request the current peer count.
@@ -419,6 +422,9 @@ async fn handle_peer_commands(
             PeerCommand::RemoveDownloadedGame { id } => {
                 handle_remove_downloaded_game_command(ctx, tx_notify_ui, id).await;
             }
+            PeerCommand::CancelDownload { id } => {
+                handle_cancel_download_command(ctx, tx_notify_ui, id).await;
+            }
             PeerCommand::SetGameDir(game_dir) => {
                 handle_set_game_dir_command(ctx, tx_notify_ui, game_dir).await;
             }