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

vitest.config.ts

@@ -0,0 +1,33 @@
+import { defineConfig } from 'vitest/config';
+import { svelte } from '@sveltejs/vite-plugin-svelte';
+import { resolve } from 'path';
+
+export default defineConfig({
+	plugins: [svelte({ hot: !process.env.VITEST })],
+	test: {
+		globals: true,
+		environment: 'jsdom',
+		setupFiles: ['./tests/setup.ts'],
+		include: ['src/**/*.{test,spec}.{js,ts}', 'tests/**/*.{test,spec}.{js,ts}'],
+		coverage: {
+			provider: 'v8',
+			reporter: ['text', 'json', 'html'],
+			exclude: [
+				'node_modules/',
+				'tests/',
+				'**/*.config.{js,ts}',
+				'**/*.d.ts',
+				'src/routes/**/+*.{js,ts,svelte}', // Exclude SvelteKit route files from coverage
+				'src/app.html'
+			]
+		}
+	},
+	resolve: {
+		alias: {
+			$lib: resolve('./src/lib'),
+			$utils: resolve('./src/utils'),
+			$models: resolve('./src/models'),
+			$types: resolve('./src/types')
+		}
+	}
+});