chore: format

0.6.38

0.6.39

0.6.40

0.6.41

- Analyze current implementation of ENABLE_CHAT_RESPONSE_BASE64_IMAGE_URL_CONVERSION
- Document how response images are converted from base64 to file URLs
- Identify missing implementation for user input images
- Explain access control for image files
- Provide solution approach for converting user input images
- Document expected performance improvements

Related to GitHub discussion open-webui#13122

This implements Phase 1 of the solution for GitHub discussion open-webui#13122,
which addresses the performance issue where large base64 images embedded
in session data cause slow load times and poor browser performance.

## Changes Made

### Backend Changes:

1. **Environment Variable** (backend/open_webui/env.py)
   - Added ENABLE_CHAT_INPUT_BASE64_IMAGE_URL_CONVERSION (default: True)
   - Controls whether user input images are converted from base64 to file URLs

2. **Image Conversion Function** (backend/open_webui/utils/files.py)
   - Added convert_message_content_images() function
   - Handles both string content (markdown) and array content (OpenAI format)
   - Converts base64 images > 1024 chars to file URLs via upload_image()
   - Returns /api/v1/files/{id}/content URLs

3. **Chat History Converter** (backend/open_webui/models/chats.py)
   - Added _convert_chat_images() helper method
   - Processes both chat.messages[] and chat.history.messages{}
   - Applies conversion to all messages with image content
   - Includes error handling to prevent conversion failures from breaking chats

4. **Router Integration** (backend/open_webui/routers/chats.py)
   - Updated create_new_chat() - converts images on chat creation
   - Updated update_chat_by_id() - converts images on chat updates
   - Updated import_chats() - converts images in imported chats
   - All endpoints now accept Request parameter for conversion

5. **Documentation** (IMAGE_STORAGE_ANALYSIS.md)
   - Added implementation summary section
   - Documented all code changes with file locations and line numbers
   - Provided configuration instructions
   - Explained how the conversion works end-to-end

## Expected Performance Improvements

- Session JSON size reduced from 100MB+ to <1MB
- Chat load time improved from several seconds to <1 second
- Images loaded on-demand with full browser caching support
- Memory usage reduced (images not kept in memory)

## Backward Compatibility

- Existing chats with base64 images continue to work
- Conversion only applies to new/updated chats
- Feature can be disabled via environment variable
- Access control enforced via existing file permissions system

Related to: open-webui#13122

- Simplified convert_message_content_images with early returns
- Reduced nesting in _convert_chat_images using helper function
- Removed redundant comments from router endpoints
- Moved module imports from function body to top of file
- Cleaner, more maintainable code structure

- Use .get() with defaults instead of isinstance before accessing
- Chain .get() calls for nested dict access
- Trust data structure with appropriate defaults
- Cleaner, more Pythonic code