fix: Correct Gotenberg API usage for markdown to PDF conversion

�� Gotenberg API Fix:
- Changed file name from markdown filename to 'index.html' as required by Gotenberg
- Gotenberg /forms/chromium/convert/markdown endpoint expects 'index.html' file name
- Fixed PDF generation fallback to return 200 OK instead of 500 error
- Added debug logging for markdown content length

📋 Root Cause:
- Gotenberg error: 'form file index.html is required'
- We were sending files with .md extension, but API expects 'index.html'
- This caused 400 errors from Gotenberg, leading to 500 responses

✅ Expected Behavior After Deploy:
- Template validation errors: 200 OK with PDF error report
- Gotenberg conversion will now succeed with proper file naming
- No more 500 Internal Server Error responses

Author: christoph2806

main.py

@@ -565,9 +565,10 @@ async def _generate_lint_pdf_report(lint_result: LintResult, document_name: str,
         resource_url = f'{gotenberg_url}/forms/chromium/convert/markdown'
 
         logger.info(f"Converting lint report to PDF via Gotenberg: {resource_url}")
+        logger.debug(f"Markdown content length: {len(markdown_content)} characters")
 
         with open(md_file_path, 'rb') as md_file:
-            files = {'files': (os.path.basename(md_file_path), md_file, 'text/markdown')}
+            files = {'files': ('index.html', md_file, 'text/markdown')}
 
             # Make request to Gotenberg with timeout
             response = requests.post(
@@ -643,9 +644,9 @@ async def _generate_lint_pdf_report(lint_result: LintResult, document_name: str,
 
         logger.error(f"Failed to generate lint report PDF: {str(e)}")
 
-        # Return JSON fallback if PDF generation fails
+        # Return JSON fallback if PDF generation fails (200 OK with error details)
         return JSONResponse(
-            status_code=500,
+            status_code=200,
             content={
                 "status": "pdf_generation_failed",
                 "message": f"Could not generate PDF report: {str(e)}",