test: add comprehensive frontend tests for components, stores, and utils

Full test coverage for the frontend implementation using Vitest and
Testing Library. Tests are organized by concern with shared fixtures.

Component tests:
- AppShell.test.tsx: Navigation tabs, view switching, batch mode overlay
- FocusCard.test.tsx: Rendering, action buttons, keyboard shortcuts, empty state
- QueueView.test.tsx: Item display, focus promotion, empty state
- QueueItem.test.tsx: Type badges, click handling
- QueueSummary.test.tsx: Count display by type
- QuickCapture.test.tsx: Modal behavior, form submission, error states
- BatchMode.test.tsx: Progress tracking, item advancement, completion
- App.test.tsx: Updated for AppShell integration

Store tests:
- focus-store.test.ts: Item management, act(), setFocus(), reorderQueue()
- nav-store.test.ts: View switching
- capture-store.test.ts: Open/close, submission states
- batch-store.test.ts: Batch lifecycle, status tracking, derived counts

Library tests:
- types.test.ts: Type guards, staleness computation
- transform.test.ts: Lore data transformation, priority ordering
- format.test.ts: IID formatting for MRs vs issues

E2E tests (app.spec.ts):
- Navigation flow
- Focus card interactions
- Queue management
- Quick capture flow

Test infrastructure:
- fixtures.ts: makeFocusItem() factory
- tauri-plugin-shell.ts: Mock for @tauri-apps/plugin-shell
- Updated tauri-api.ts mock with new commands
- vitest.config.ts: Path aliases, jsdom environment
- playwright.config.ts: Removed webServer (run separately)
- package.json: Added @tauri-apps/plugin-shell dependency

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/helpers/fixtures.ts

@@ -0,0 +1,25 @@
+/**
+ * Shared test fixtures for Mission Control frontend tests.
+ *
+ * Centralized here to avoid duplication across test files.
+ */
+
+import type { FocusItem } from "@/lib/types";
+
+/** Create a FocusItem with sensible defaults, overridable per field. */
+export function makeFocusItem(
+  overrides: Partial<FocusItem> = {}
+): FocusItem {
+  return {
+    id: "mr_review:platform/core:847",
+    title: "Fix authentication token refresh logic",
+    type: "mr_review",
+    project: "platform/core",
+    url: "https://gitlab.com/platform/core/-/merge_requests/847",
+    iid: 847,
+    updatedAt: new Date().toISOString(),
+    contextQuote: null,
+    requestedBy: null,
+    ...overrides,
+  };
+}