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

svelte.config.js

@@ -10,7 +10,11 @@ const config = {
 		// adapter-auto only supports some environments, see https://kit.svelte.dev/docs/adapter-auto for a list.
 		// If your environment is not supported or you settled on a specific environment, switch out the adapter.
 		// See https://kit.svelte.dev/docs/adapters for more information about adapters.
-		adapter: adapter()
+		adapter: adapter(),
+		alias: {
+			$models: 'src/models',
+			$utils: 'src/utils'
+		}
 	}
 };