Phase 1: Add pgqueuer infrastructure

- Add pgqueuer dependency to pyproject.toml
- Create worker.py with schema installation and job handler registration
- Add make worker command to Makefile
- Update make dev to run worker alongside backend/frontend
- Use has_table() check for idempotent schema installation
- Register 'random_number' job handler (placeholder that logs for now)

backend/pyproject.toml

@@ -11,7 +11,7 @@ dependencies = [
     "python-jose[cryptography]>=3.3.0",
     "email-validator>=2.0.0",
     "bech32>=1.2.0",
-    "pgqueuer>=0.1.0",
+    "pgqueuer>=0.14.0",
 ]
 
 [dependency-groups]