Phase 1: Add pgqueuer infrastructure and worker skeleton

- Add pgqueuer dependency to pyproject.toml
- Create worker.py with basic setup:
  - Independent database connection using asyncpg
  - Install pgqueuer schema on startup
  - Register dummy job handler
  - Start consumer loop
- Add 'make worker' command
- Update 'make dev' to run worker alongside backend/frontend

Validation:
- Worker starts successfully
- pgqueuer tables exist in database
- All existing tests pass

backend/worker.py

@@ -0,0 +1,62 @@
+"""Worker process for processing async jobs using pgqueuer."""
+
+import asyncio
+import logging
+import os
+
+import asyncpg
+from pgqueuer import AsyncpgDriver, PgQueuer, Queries
+
+logging.basicConfig(level=logging.INFO)
+logger = logging.getLogger(__name__)
+
+# Get DATABASE_URL and convert from SQLAlchemy format (postgresql+asyncpg://)
+# to asyncpg format (postgresql://)
+_raw_db_url = os.getenv(
+    "DATABASE_URL", "postgresql+asyncpg://postgres:postgres@localhost:5432/arbret"
+)
+DATABASE_URL = _raw_db_url.replace("postgresql+asyncpg://", "postgresql://")
+
+
+async def main() -> None:
+    """Main worker loop."""
+    logger.info("Starting worker...")
+
+    # Connect to database independently
+    conn = await asyncpg.connect(DATABASE_URL)
+    driver = AsyncpgDriver(conn)
+
+    # Install pgqueuer schema (creates tables if they don't exist)
+    queries = Queries.from_asyncpg_connection(conn)
+    try:
+        await queries.install()
+        logger.info("pgqueuer schema installed")
+    except Exception as e:
+        # Schema might already exist, which is fine
+        if "already exists" in str(e).lower():
+            logger.info("pgqueuer schema already exists")
+        else:
+            raise
+
+    # Initialize pgqueuer
+    pgq = PgQueuer(connection=driver)
+
+    # Register job handlers using entrypoint decorator
+    @pgq.entrypoint("dummy")  # type: ignore[type-var]
+    async def dummy_job_handler(payload: dict) -> None:
+        """Dummy job handler for testing."""
+        logger.info(f"Processing dummy job with payload: {payload}")
+
+    logger.info("Worker started, waiting for jobs...")
+
+    # Start consuming jobs
+    try:
+        await pgq.run()
+    except KeyboardInterrupt:
+        logger.info("Worker shutting down...")
+    finally:
+        await conn.close()
+
+
+if __name__ == "__main__":
+    asyncio.run(main())