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/README.md

@@ -14,7 +14,8 @@ It is designed to run headless – other crates (most notably
   roots are announced or served.
 - `PeerCommand` represents the small control surface exposed to the UI layer:
   `ListGames`, `GetGame`, `FetchLatestFromPeers`, `DownloadGameFiles`,
-  `InstallGame`, `UninstallGame`, `SetGameDir`, and `GetPeerCount`.
+  `InstallGame`, `UninstallGame`, `RemoveDownloadedGame`, `CancelDownload`,
+  `SetGameDir`, and `GetPeerCount`.
 - `PeerEvent` enumerates everything the peer runtime reports back to the UI:
   library snapshots, download/install/uninstall lifecycle updates, runtime
   failures, and peer membership changes.
@@ -82,6 +83,11 @@ When the UI asks to download a game:
 6. After a successful sentinel commit, `PeerEvent::DownloadGameFilesFinished`
    is emitted and the peer auto-runs the install transaction.
 
+`PeerCommand::CancelDownload` cancels the tracked download token for an active
+transfer. The transfer task remains responsible for clearing `active_operations`,
+so the UI continues to treat active-operation snapshots as the single source of
+truth for whether a download is still running.
+
 ### Install Transactions
 
 Install, update, uninstall, downloaded-file removal, and startup recovery live