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

package.json

@@ -8,21 +8,33 @@
 		"build": "vite build",
 		"preview": "vite preview",
 		"check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
-		"check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch"
+		"check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch",
+		"test": "vitest run",
+		"test:watch": "vitest",
+		"test:ui": "vitest --ui",
+		"test:coverage": "vitest run --coverage",
+		"test:e2e": "playwright test",
+		"test:e2e:ui": "playwright test --ui"
 	},
 	"packageManager": "pnpm@9.0.0",
 	"devDependencies": {
 		"@auth/core": "^0.40.0",
+		"@playwright/test": "^1.56.1",
 		"@sveltejs/adapter-auto": "^6.1.0",
 		"@sveltejs/kit": "^2.37.0",
 		"@sveltejs/vite-plugin-svelte": "^6.1.3",
+		"@testing-library/jest-dom": "^6.9.1",
+		"@testing-library/svelte": "^5.2.9",
 		"@types/node": "^22.12.0",
 		"@types/node-cron": "^3.0.11",
+		"@vitest/ui": "^4.0.10",
+		"jsdom": "^27.2.0",
 		"svelte": "^5.38.6",
 		"svelte-check": "^4.0.0",
 		"tslib": "^2.6.0",
 		"typescript": "^5.1.6",
-		"vite": "^7.1.3"
+		"vite": "^7.1.3",
+		"vitest": "^4.0.10"
 	},
 	"dependencies": {
 		"@auth/sveltekit": "^1.10.0",