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-tauri-deno-ts/tests/gameState.test.ts

@@ -1,7 +1,15 @@
 import {
     actionLabel,
     activeStatusById,
+    applyFilterAndSort,
+    countByFilter,
+    deriveState,
+    downloadProgressPercent,
+    formatDownloadBytes,
     formatBytesPerSecond,
+    formatDownloadEta,
+    formatDownloadSpeed,
+    formatDownloadSpeedShort,
     mergeGameUpdate,
 } from '../src/lib/gameState.ts';
 import {
@@ -134,3 +142,62 @@ Deno.test('downloading action label includes current speed', () => {
         'download label should include speed',
     );
 });
+
+Deno.test('downloading state is distinct and stays on the local filter', () => {
+    const downloading = game({
+        id: 'downloading',
+        name: 'Downloading',
+        install_status: InstallStatus.Downloading,
+    });
+    const local = game({
+        id: 'local',
+        name: 'Local',
+        downloaded: true,
+    });
+    const remote = game({
+        id: 'remote',
+        name: 'Remote',
+        peer_count: 1,
+    });
+
+    assertEquals(
+        deriveState(downloading),
+        'downloading',
+        'download operation should render the dedicated downloading state',
+    );
+    assertEquals(
+        countByFilter([downloading, local, remote]).local,
+        2,
+        'local filter count should include in-flight downloads',
+    );
+    assertEquals(
+        applyFilterAndSort([downloading, local, remote], 'local', 'status', '').length,
+        2,
+        'local filter should include in-flight downloads',
+    );
+});
+
+Deno.test('download progress formatting matches the progress-bar layouts', () => {
+    const downloading = game({
+        install_status: InstallStatus.Downloading,
+        download_progress: {
+            downloaded_bytes: 12 * 1024 * 1024 * 1024,
+            total_bytes: 35 * 1024 * 1024 * 1024,
+            bytes_per_second: 49_400_000,
+        },
+    });
+
+    assertEquals(
+        Math.round(downloadProgressPercent(downloading)),
+        34,
+        'progress percent should come from backend byte counters',
+    );
+    assertEquals(formatDownloadSpeed(49_400_000), '49.4 MB/s', 'large bar speed format');
+    assertEquals(formatDownloadSpeedShort(49_400_000), '49 MB/s', 'card speed format');
+    assertEquals(
+        formatDownloadBytes(12 * 1024 * 1024 * 1024),
+        '12 GB',
+        'downloaded byte format should avoid noisy trailing decimals',
+    );
+    assertEquals(formatDownloadEta(485), '8 min', 'eta format should stay compact');
+});