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/tests/gameState.test.ts

@@ -2,6 +2,7 @@ import {
     actionLabel,
     activeStatusById,
     applyFilterAndSort,
+    canStreamInstall,
     countByFilter,
     deriveState,
     downloadProgressPercent,
@@ -209,3 +210,36 @@ Deno.test('download progress formatting matches the progress-bar layouts', () =>
     );
     assertEquals(formatDownloadEta(485), '8 min', 'eta format should stay compact');
 });
+
+Deno.test('stream install is available only for idle remote games', () => {
+    assertEquals(
+        canStreamInstall(game({ downloaded: false, installed: false, peer_count: 1 })),
+        true,
+        'remote-only idle games should allow streamed install',
+    );
+    assertEquals(
+        canStreamInstall(game({ downloaded: true, installed: false, peer_count: 1 })),
+        false,
+        'downloaded games should install from local archives',
+    );
+    assertEquals(
+        canStreamInstall(game({ downloaded: false, installed: true, peer_count: 1 })),
+        false,
+        'installed games should not expose streamed install',
+    );
+    assertEquals(
+        canStreamInstall(game({ downloaded: false, installed: false, peer_count: 0 })),
+        false,
+        'games without peers should not expose streamed install',
+    );
+    assertEquals(
+        canStreamInstall(game({
+            downloaded: false,
+            installed: false,
+            peer_count: 1,
+            install_status: InstallStatus.CheckingPeers,
+        })),
+        false,
+        'busy games should not expose streamed install',
+    );
+});