fix: Prevent fallback to 400 errors when linting fails

🔧 Core Issue Resolution:
- Changed exception handling in linting stage to return 200 OK instead of continuing processing
- When linting service fails (e.g., PDF generation issues), return JSON error response with 200 status
- Prevents fallback to normal template processing that results in 400 Bad Request errors

📋 Changes:
- Modified exception handler to return JSONResponse with 200 status on linting failures
- Added detailed error logging with traceback for debugging
- Ensures file cleanup on linting service errors
- Provides clear error message indicating likely template validation issues

✅ Expected Behavior:
- Template validation errors: 200 OK with PDF error report
- Linting service errors: 200 OK with JSON error message
- No more 400 Bad Request responses for template validation issues

Author: christoph2806

main.py

@@ -938,8 +938,26 @@ async def process_document_template(
 
         except Exception as e:
             logger.error(f"Template linting failed: {str(e)}")
-            # Don't block processing on linting errors - just log and continue
-            logger.warning("Continuing with template processing despite linting failure")
+            logger.error(f"Linting error traceback: {traceback.format_exc()}")
+            
+            # Clean up uploaded file
+            if os.path.exists(file_path):
+                os.remove(file_path)
+            
+            # For linting failures, return JSON error response as fallback
+            return JSONResponse(
+                status_code=200,
+                content={
+                    "status": "linting_service_error",
+                    "message": f"Template linting service failed: {str(e)}",
+                    "error_type": "linting_service_error",
+                    "details": {
+                        "filename": file.filename,
+                        "linting_error": str(e),
+                        "suggestion": "The template likely has validation errors. Check template syntax and try again."
+                    }
+                }
+            )
 
         # Stage 2: Template Loading and Image Processing
         try: