Refactor OpenAPI fetcher for improved clarity and robustness

Reorganized and enhanced the OpenAPI fetch logic for better maintainability and error handling. Key updates include improved environment variable validation, more detailed error messages, streamlined configuration loading, and additional safety checks for file paths and directories. Added proper logging and ensured the process flow is easy to trace.

backend/app/database.py

@@ -48,10 +48,19 @@ def load_slots_data(session: Session):
     from .data import slots
     from .data import proposals
 
-    if not session.query(models.Slot).first():  # Load only if no slots exist
-        session.add_all(slots)
-        session.add_all(proposals)
-        session.commit()
+    # Only load data if slots are missing
+    if not session.query(models.Slot).first():
+        session.add_all(slots)  # Add slots
+        print("[INFO] Seeding slots...")
+
+    # Check if proposals table is empty and seed proposals
+    if not session.query(models.Proposal).first():
+        session.add_all(proposals)  # Add proposals
+        print("[INFO] Seeding proposals...")
+
+    # Commit all changes to the database
+    session.commit()
+    print("[INFO] Seeding complete.")
 
 
 # Load full sample data (used in dev/test)