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/unit/middleware/auth.test.ts

@@ -0,0 +1,132 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { requireAuth, optionalAuth } from '$lib/server/middleware/auth';
+
+describe('auth middleware', () => {
+	describe('requireAuth', () => {
+		it('should return user when authenticated', async () => {
+			const mockLocals = {
+				auth: vi.fn().mockResolvedValue({
+					user: {
+						nickname: 'testuser',
+						name: 'Test User',
+						email: 'test@example.com',
+						image: 'https://example.com/avatar.jpg'
+					}
+				})
+			};
+
+			const user = await requireAuth(mockLocals as any);
+
+			expect(user).toEqual({
+				nickname: 'testuser',
+				name: 'Test User',
+				email: 'test@example.com',
+				image: 'https://example.com/avatar.jpg'
+			});
+		});
+
+		it('should throw 401 error when no session', async () => {
+			const mockLocals = {
+				auth: vi.fn().mockResolvedValue(null)
+			};
+
+			await expect(requireAuth(mockLocals as any)).rejects.toThrow();
+		});
+
+		it('should throw 401 error when no user in session', async () => {
+			const mockLocals = {
+				auth: vi.fn().mockResolvedValue({})
+			};
+
+			await expect(requireAuth(mockLocals as any)).rejects.toThrow();
+		});
+
+		it('should throw 401 error when no nickname in user', async () => {
+			const mockLocals = {
+				auth: vi.fn().mockResolvedValue({
+					user: {
+						name: 'Test User'
+					}
+				})
+			};
+
+			await expect(requireAuth(mockLocals as any)).rejects.toThrow();
+		});
+
+		it('should handle user with only nickname', async () => {
+			const mockLocals = {
+				auth: vi.fn().mockResolvedValue({
+					user: {
+						nickname: 'testuser'
+					}
+				})
+			};
+
+			const user = await requireAuth(mockLocals as any);
+
+			expect(user).toEqual({
+				nickname: 'testuser',
+				name: undefined,
+				email: undefined,
+				image: undefined
+			});
+		});
+	});
+
+	describe('optionalAuth', () => {
+		it('should return user when authenticated', async () => {
+			const mockLocals = {
+				auth: vi.fn().mockResolvedValue({
+					user: {
+						nickname: 'testuser',
+						name: 'Test User',
+						email: 'test@example.com'
+					}
+				})
+			};
+
+			const user = await optionalAuth(mockLocals as any);
+
+			expect(user).toEqual({
+				nickname: 'testuser',
+				name: 'Test User',
+				email: 'test@example.com',
+				image: undefined
+			});
+		});
+
+		it('should return null when no session', async () => {
+			const mockLocals = {
+				auth: vi.fn().mockResolvedValue(null)
+			};
+
+			const user = await optionalAuth(mockLocals as any);
+
+			expect(user).toBeNull();
+		});
+
+		it('should return null when no user in session', async () => {
+			const mockLocals = {
+				auth: vi.fn().mockResolvedValue({})
+			};
+
+			const user = await optionalAuth(mockLocals as any);
+
+			expect(user).toBeNull();
+		});
+
+		it('should return null when no nickname in user', async () => {
+			const mockLocals = {
+				auth: vi.fn().mockResolvedValue({
+					user: {
+						name: 'Test User'
+					}
+				})
+			};
+
+			const user = await optionalAuth(mockLocals as any);
+
+			expect(user).toBeNull();
+		});
+	});
+});