Refactor: Continuous conversation, UI improvements, and build fixes

Merge branch 'main' of https://huggingface.co/spaces/colearn30/colearn30-ai-grading-agents into main

Update frontend/src/types/index.ts

Update frontend/src/App.tsx

feat: add continuous conversation, relax prompt constraints, and fix docker config

Update frontend/src/App.tsx

Update frontend/src/types/index.ts

Update frontend/src/App.tsx

Update frontend/src/App.tsx

feat: Add grading progress modal with assistant info

feat: Refactor assistant system with auto-matching and manual selection

Add missing password protection files

Add password protection system

fix: Reorganize header layout and fix API docs link

feat: Add 批改心法課程 link to header navigation

feat: Add header navigation with Assistant guide and API docs

feat: Complete AI grading platform with multilingual support