fix bug related to export error and UI changes for more intuitive.

Fixed project conversation pagination (cursor + limit)
Read preview chats from the sidebar API (up to 100 per project)
Map gizmo_id from the main list → project folder
Resolve project folder from full conversation payload after download
Add conversation_count per project in chatgpt/export-index.json for debugging

ChatGPT Project knowledge files — PDFs and docs uploaded to a Project export to projects/{Name}/knowledge-files/
Project custom instructions — saved as custom-instructions.txt and instructions.md per Project
project.json + knowledge-manifest.json — metadata and download index for each Project folder

Fixed Gemini export bug, and added feedback section.