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

playwright.config.ts

@@ -0,0 +1,15 @@
+import type { PlaywrightTestConfig } from '@playwright/test';
+
+const config: PlaywrightTestConfig = {
+	webServer: {
+		command: 'npm run build && npm run preview',
+		port: 4173
+	},
+	testDir: 'tests/e2e',
+	testMatch: /(.+\.)?(test|spec)\.[jt]s/,
+	use: {
+		baseURL: 'http://localhost:4173'
+	}
+};
+
+export default config;