fix: restore finally block in handle_db_errors to prevent connection leaks (#38)

Reviewer correctly identified that removing the finally block introduced
real connection leaks for handlers that do not call db.close() on their
own error paths. Peewee's PooledDatabase.close() is a no-op on the second
call, so double-close is harmless — the finally block provides necessary
safety net.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/dependencies.py

@@ -800,6 +800,14 @@ def handle_db_errors(func):
                 logger.info(f"Database rollback successful for {func_name}")
             except Exception as rollback_error:
                 logger.error(f"Rollback failed in {func_name}: {rollback_error}")
+            finally:
+                try:
+                    db.close()
+                    logger.info(f"Database connection closed for {func_name}")
+                except Exception as close_error:
+                    logger.error(
+                        f"Error closing database connection in {func_name}: {close_error}"
+                    )
 
             raise HTTPException(
                 status_code=500, detail=f"Database error in {func_name}: {str(e)}"