Add job processing system with streaming endpoint

Introduced a `processing` router to handle job streaming using server-sent events. Added `Jobs` and `JobStatus` models for managing job-related data, along with database creation logic. Updated the `sample` router to create new job entries during experiment creation.

backend/main.py

@@ -235,7 +235,7 @@ if __name__ == "__main__":
     if is_ci or environment == "test":
         # Test or CI Mode: Run server process temporarily for test validation
         ssl_dir = Path(cert_path).parent
-        ssl_dir.mkdir(parents=True, exist_ok=True)
+        # ssl_dir.mkdir(parents=True, exist_ok=True)
 
         # Generate self-signed certs if missing
         if not Path(cert_path).exists() or not Path(key_path).exists():