feat(tauri): add low-disk streamed install action

NEXT_STEPS item 1 called out that streamed install was still CLI-only
because the Tauri app started the peer with no stream provider. Users can now
choose an explicit "Low disk install" action from the game detail modal for
remote-only games instead of taking the default archive-preserving download
path.

The GUI command queues a normal peer detail fetch first so the peer database
has the file metadata needed for source validation. A small pending handoff in
Tauri routes the resulting GotGameFiles event into StreamInstallGame instead
of DownloadGameFiles, and clears that pending state on no-peer or download
failure events. This keeps the existing download continuation untouched for
the default action.

The external unrar stream provider moved from the CLI harness into
lanspread-peer so CLI and Tauri use the same implementation. Tauri resolves
the bundled unrar sidecar path and injects that provider at peer startup;
falling back to the noop provider keeps peer startup alive if the sidecar
cannot be resolved, while the streamed install operation still fails safely.

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

Refs: NEXT_STEPS.md item 1

crates/lanspread-tauri-deno-ts/src/windows/MainWindow.tsx

@@ -192,6 +192,7 @@ export const MainWindow = () => {
                     thumbnailUrl={thumbnails.get(openGame.id)}
                     onClose={() => setOpenGameId(null)}
                     onPrimary={handlePrimary}
+                    onStreamInstall={(g) => actions.streamInstall(g.id)}
                     onUninstall={handleUninstall}
                     onRemoveDownload={handleRemoveDownload}
                     onCancelDownload={(g) => actions.cancelDownload(g.id)}