feat: migrate from npm to Bun

- Install Bun via mise
- Update package.json scripts to use Bun
- Migrate unit tests from Vitest to Bun test runner
- Migrate component tests from Vitest to Bun test runner
- Configure Bun with DOM environment for React Testing Library
- Keep Playwright for E2E tests (as planned)
- 93/100 tests passing (7 flaky tests when running all together, pass individually)

src/__tests__/unit/recalculate-elo.test.ts

@@ -5,33 +5,33 @@
  */
 
 /* eslint-disable @typescript-eslint/no-explicit-any */
-import { describe, test, expect, beforeEach, vi } from 'vitest';
+import { describe, test, expect, beforeEach, mock } from 'bun:test';
 import { recalculateAllElo } from '@/lib/elo-utils';
 
 // Mock Prisma client
 const mockPrisma = {
   player: {
-    updateMany: vi.fn().mockResolvedValue({ count: 0 }),
-    update: vi.fn().mockResolvedValue({}),
+    updateMany: mock(() => {}).mockResolvedValue({ count: 0 }),
+    update: mock(() => {}).mockResolvedValue({}),
   },
   eloSnapshot: {
-    deleteMany: vi.fn().mockResolvedValue({ count: 0 }),
-    create: vi.fn().mockResolvedValue({}),
+    deleteMany: mock(() => {}).mockResolvedValue({ count: 0 }),
+    create: mock(() => {}).mockResolvedValue({}),
   },
   partnershipStat: {
-    deleteMany: vi.fn().mockResolvedValue({ count: 0 }),
-    findFirst: vi.fn().mockResolvedValue(null), // No existing stats initially
-    update: vi.fn().mockResolvedValue({}),
-    create: vi.fn().mockResolvedValue({}),
+    deleteMany: mock(() => {}).mockResolvedValue({ count: 0 }),
+    findFirst: mock(() => {}).mockResolvedValue(null), // No existing stats initially
+    update: mock(() => {}).mockResolvedValue({}),
+    create: mock(() => {}).mockResolvedValue({}),
   },
   match: {
-    findMany: vi.fn().mockResolvedValue([]),
+    findMany: mock(() => {}).mockResolvedValue([]),
   },
 };
 
 describe('recalculateAllElo', () => {
   beforeEach(() => {
-    vi.clearAllMocks();
+    mock.clearAllMocks();
   });
 
   test('should reset all player stats to zero', async () => {