feat: migrate imphnen-backend-hackathon into workspace as imphnen-hackathon crate

Consolidates the standalone hackathon backend (16 crates) into a single
imphnen-hackathon crate following the existing clean architecture patterns.
All endpoints are exposed under /v1/hackathon/ via the gateway.

Features migrated:
- Auth: Supabase-based signup/login/GitHub OAuth/password reset (own JWT)
- Users: profile management with team listing
- Teams: CRUD with city validation, deadline enforcement, invite system
- Invitations: team member invitations with accept/reject flow
- Join Requests: team join request workflow
- Chat: team messaging with author/leader delete permissions
- Submissions: project submission lifecycle (draft→pending→submitted)
- Storage: Supabase Storage file upload endpoints
- Certificates: public user certificate data endpoint
- Winners: public winners listing
- Admin: admin-only CRUD for all entities

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -21,14 +21,30 @@ MINIO_SECRET_KEY=minioadmin
 MINIO_SECURE=false
 
 GOOGLE_CLIENT_ID="your_google_client_id"
-GOOGLE_CLIENT_SECRET="your_google_client_secret"
-POOL_SIZE=10
-CONNECT_TIMEOUT=30
-IDLE_TIMEOUT=60
-MAX_LIFETIME=1800
-STATEMENT_TIMEOUT=30000
-IDLE_IN_TRANSACTION_SESSION_TIMEOUT=60000
-SSLMODE=require
-RETRY_ATTEMPTS=3
-RETRY_DELAY=1
+GOOGLE_CLIENT_SECRET="your_google_client_secret"
+POOL_SIZE=10
+CONNECT_TIMEOUT=30
+IDLE_TIMEOUT=60
+MAX_LIFETIME=1800
+STATEMENT_TIMEOUT=30000
+IDLE_IN_TRANSACTION_SESSION_TIMEOUT=60000
+SSLMODE=require
+RETRY_ATTEMPTS=3
+RETRY_DELAY=1
 GOOGLE_REDIRECT_URL=http://localhost:8000/api/v1/auth/google/callback
+
+# Hackathon feature
+HACKATHON_JWT_SECRET=your-hackathon-jwt-secret-at-least-32-chars
+HACKATHON_JWT_EXPIRY_HOURS=168
+HACKATHON_SUPABASE_URL=https://your-project.supabase.co
+HACKATHON_SUPABASE_ANON_KEY=your-supabase-anon-key
+HACKATHON_SUPABASE_SERVICE_ROLE_KEY=your-supabase-service-role-key
+HACKATHON_STORAGE_BUCKET=hackathon-uploads
+HACKATHON_GITHUB_CLIENT_ID=your-github-client-id
+HACKATHON_GITHUB_CLIENT_SECRET=your-github-client-secret
+HACKATHON_GITHUB_REDIRECT_URL=http://localhost:8080/v1/hackathon/auth/github/callback
+HACKATHON_SMTP_HOST=smtp.gmail.com
+HACKATHON_SMTP_USER=your-email@gmail.com
+HACKATHON_SMTP_PASSWORD=your-smtp-password
+HACKATHON_FROM_EMAIL=noreply@yourdomain.com
+HACKATHON_FRONTEND_URL=https://hackathon.imphnen.dev