🔍 Add INFO-level diff debugging to investigate empty PatchSet

🐛 INVESTIGATION:
- Unidiff PatchSet is empty despite 16,951 characters of diff content
- Both unidiff and manual parser returning 0 files

🔍 DEBUG IMPROVEMENTS:
- Show PatchSet file count at INFO level (not DEBUG)
- When PatchSet is empty, display:
  - First 1000 characters of diff content
  - Total line count
  - First 10 lines of diff for pattern analysis
- Use repr() to show exact content including hidden characters

📊 EXPECTED OUTPUT:
Next run should show exactly what the diff content looks like
and help identify why unidiff can't parse any files from it.

Author: truongnh1992

gemini_reviewer/diff_parser.py

@@ -66,7 +66,16 @@ def _parse_with_unidiff(self, diff_content: str) -> List[DiffFile]:
         """Parse diff using the unidiff library."""
         try:
             patch_set = PatchSet(diff_content)
-            logger.debug(f"Unidiff PatchSet created with {len(patch_set)} files")
+            logger.info(f"🔍 Unidiff PatchSet created with {len(patch_set)} files")
+            
+            # If no files found, show diff preview for debugging
+            if len(patch_set) == 0:
+                logger.warning(f"PatchSet is empty! Diff preview (first 1000 chars):")
+                logger.warning(f"Diff content: {repr(diff_content[:1000])}")
+                lines = diff_content.split('\n')
+                logger.warning(f"Total lines: {len(lines)}")
+                logger.warning(f"First 10 lines: {lines[:10]}")
+                
             diff_files = []
 
             for i, patched_file in enumerate(patch_set):