Add Vitest unit tests and Playwright e2e suite for frontend

Replaces the ad-hoc test-e2e.mjs scripts with a proper test stack:
Vitest covers $lib (api, auth, signalr) with mocked fetch/SignalR/navigation,
and @playwright/test covers auth, stores, lists, recipes, and SignalR realtime
sync between two browser contexts. Tests use uniqueName() for every entity
since the backend has no per-test reset.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -10,6 +10,13 @@ node_modules/
 build/
 .svelte-kit/
 
+## Playwright
+playwright-report/
+test-results/
+
+## Claude Code (local agent state)
+.claude/
+
 ## Environment
 .env