refactor: consolidate formatting utilities and add testing infrastructure

- Replace 8 duplicate formatCurrency functions with shared utility
- Add comprehensive formatter utilities (currency, date, number, etc.)
- Set up Vitest for unit testing with 38 passing tests
- Set up Playwright for E2E testing
- Consolidate database connection to single source (src/utils/db.ts)
- Add auth middleware helpers to reduce code duplication
- Fix display bug: remove spurious minus sign in recent activity amounts
- Add path aliases for cleaner imports ($utils, $models)
- Add project documentation (CODEMAP.md, REFACTORING_PLAN.md)

Test coverage: 38 unit tests passing
Build: successful with no breaking changes

tests/setup.ts

@@ -0,0 +1,12 @@
+import '@testing-library/jest-dom/vitest';
+import { vi } from 'vitest';
+
+// Mock environment variables
+process.env.MONGO_URL = 'mongodb://localhost:27017/test';
+process.env.AUTH_SECRET = 'test-secret';
+process.env.AUTHENTIK_ID = 'test-client-id';
+process.env.AUTHENTIK_SECRET = 'test-client-secret';
+process.env.AUTHENTIK_ISSUER = 'https://test.authentik.example.com';
+
+// Mock SvelteKit specific globals
+global.fetch = vi.fn();