Refactor golden image handling in backup upload process</message>

<message>Update the _set_golden_from_path function to improve the handling of existing golden image files. Replace the existing unlink logic with a more robust method that safely removes files or broken symlinks using the missing_ok parameter. This change enhances the reliability of the backup upload process by ensuring that stale references are properly cleared before setting a new golden image path.

backup-from-device/gnss-guard/tm-gnss-guard/server/database.py

@@ -0,0 +1,105 @@
+#!/usr/bin/env python3
+"""
+Database connection and session management for GNSS Guard Server
+"""
+
+import logging
+from contextlib import contextmanager
+from typing import Generator
+
+from sqlalchemy import create_engine, event
+from sqlalchemy.orm import sessionmaker, Session
+from sqlalchemy.pool import QueuePool
+
+from config import get_config
+from models import Base
+
+logger = logging.getLogger("gnss_guard.server.database")
+
+# Global engine and session factory
+_engine = None
+_SessionLocal = None
+
+
+def get_engine():
+    """Get or create the database engine"""
+    global _engine
+    
+    if _engine is None:
+        config = get_config()
+        
+        # Check if using SQLite (local development)
+        is_sqlite = config.database_url.startswith("sqlite")
+        
+        if is_sqlite:
+            # SQLite-specific settings
+            from sqlalchemy.pool import StaticPool
+            _engine = create_engine(
+                config.database_url,
+                connect_args={"check_same_thread": False},
+                poolclass=StaticPool,
+                echo=config.debug,
+            )
+            logger.info(f"SQLite database engine created: {config.database_url}")
+        else:
+            # PostgreSQL with connection pooling
+            _engine = create_engine(
+                config.database_url,
+                poolclass=QueuePool,
+                pool_size=5,
+                max_overflow=10,
+                pool_pre_ping=True,  # Verify connections before using
+                echo=config.debug,
+            )
+            logger.info(f"Database engine created for: {config.database_url.split('@')[-1]}")
+    
+    return _engine
+
+
+def get_session_factory():
+    """Get or create the session factory"""
+    global _SessionLocal
+    
+    if _SessionLocal is None:
+        engine = get_engine()
+        _SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+    
+    return _SessionLocal
+
+
+def init_db():
+    """Initialize database - create all tables"""
+    engine = get_engine()
+    Base.metadata.create_all(bind=engine)
+    logger.info("Database tables created/verified")
+
+
+def get_db() -> Generator[Session, None, None]:
+    """
+    Dependency for FastAPI to get database session.
+    Yields a session and ensures it's closed after use.
+    """
+    SessionLocal = get_session_factory()
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()
+
+
+@contextmanager
+def get_db_session() -> Generator[Session, None, None]:
+    """
+    Context manager for database sessions (for use outside FastAPI dependencies).
+    """
+    SessionLocal = get_session_factory()
+    db = SessionLocal()
+    try:
+        yield db
+        db.commit()
+    except Exception:
+        db.rollback()
+        raise
+    finally:
+        db.close()
+