chore: Add format detection logging for debugging

Logs the detected image format when a file is rejected to help
diagnose why iPhone uploads are being rejected.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

starpunk/media.py

@@ -170,7 +170,15 @@ def validate_image(file_data: bytes, filename: str) -> Tuple[bytes, str, int, in
             mime_type = 'image/jpeg'
 
         if mime_type not in ALLOWED_MIME_TYPES:
-            raise ValueError(f"Invalid image format. Accepted: JPEG, PNG, GIF, WebP")
+            # Log the detected format for debugging (v1.4.2)
+            try:
+                current_app.logger.warning(
+                    f'Media upload rejected format: filename="{filename}", '
+                    f'detected_format="{img.format}", mime_type="{mime_type}"'
+                )
+            except RuntimeError:
+                pass  # Outside app context
+            raise ValueError(f"Invalid image format '{img.format}'. Accepted: JPEG, PNG, GIF, WebP")
     else:
         raise ValueError("Could not determine image format")