Fix ThinkFlow output flows and update documentation

[akualubi]

Bug Fixes

• Fixed incorrect mind map generation.
• Fixed image QA failures in VLM mode.
• Fixed KeyError: 'JPEG' when exporting PPT to PDF.
• Fixed Chinese character rendering issues in PPT exports.
• Improved handling of TTS 429 rate-limit errors with enhanced retry logic.
• Fixed missing ffmpeg / ffprobe dependency issues in the video synthesis pipeline.
• Fixed status overwrite issues in the Paper2Video generation workflow.

Documentation

• Added extensive screenshots covering most UI features and actions.
• Expanded the environment setup guide with more detailed configuration instructions.