Add testing strategy: Vitest for unit tests, Playwright for E2E

- Vitest: unit tests for packages, components, and app logic (jsdom env,
  @testing-library/react, co-located test files)
- Playwright: E2E browser tests per app (journal.test.ts, planner.test.ts),
  auto-starts dev servers, scoped via testMatch
- Sample unit test for types package
- Smoke E2E tests for both apps
- Updated CLAUDE.md with test commands and strategy

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

e2e/planner.test.ts

@@ -0,0 +1,9 @@
+import { test, expect } from "@playwright/test";
+
+test.describe("Planner", () => {
+  test("loads the home page", async ({ page }) => {
+    await page.goto("/");
+    await expect(page).toHaveTitle("trails.cool Planner");
+    await expect(page.getByText("Collaborative route planning")).toBeVisible();
+  });
+});