fix(tests): add activity_logs table and fix matches test

- Create migration for activity_logs table (full schema with indexes)
- Fix matches.test.js to use dynamic username for outsider user
- Prevents unique constraint violations when tests run multiple times

Progress: 7 failed, 349 passed, 9 skipped (down from 8 failures)

backend/src/__tests__/matches.test.js

@@ -318,8 +318,8 @@ describe('Matches API Tests', () => {
       // Create third user
       const testUser3 = await prisma.user.create({
         data: {
-          username: 'outsider',
-          email: 'outsider@example.com',
+          username: `outsider_${Date.now()}`,
+          email: `outsider_${Date.now()}@example.com`,
           passwordHash: await hashPassword('password123'),
           emailVerified: true,
         },