Summary

This PR combines two related ThinkFlow upgrades:

1. A flashcard workflow refresh with generation controls, citations, and a smoother animated study experience.
2. A first usable editable PPT path backed by vendored PresentAgent, plus optional ONLYOFFICE online editing for
   generated PPTX files.

It also hardens the ONLYOFFICE integration so local development works through the frontend proxy without leaking
internal API keys into document URLs.

Flashcards

• Adds generation controls to the flashcard output flow.
• Improves the study UX with citation-aware content and animated transitions.
• Updates the flashcard study surfaces so users can generate, review, and study more naturally inside the
  workspace.
• Keeps the English and Chinese frontends aligned for the updated flashcard experience.

Editable PresentAgent PPT

• Vendors the PresentAgent runtime under vendor/presentagent.
• Adds EditablePPTService as a dedicated backend wrapper for the editable PPT pipeline.
• Introduces editable_ppt as a first-class output type in outputs-v2.
• Persists generated PPTX, deck IR, slide IR, and run metadata under the notebook output directory.
• Adds a separate editable PPT workspace in the Chinese frontend.
• Keeps PPTX download fallback available when ONLYOFFICE is not configured.

ONLYOFFICE Integration

• Adds backend endpoints for:
  • editable PPTX editor config
  • PPTX download
  • save callback
  • editable IR updates
• Adds a real same-origin online-editor-frame.html to host the editor logic.
• Proxies Document Server assets through Vite /onlyoffice in local development.
• Configures ONLYOFFICE cache URLs so they stay on the frontend origin instead of jumping to localhost:8082.
• Uses per-open editor_session_id and document-key versioning to avoid stale editor sessions.
• Normalizes generated PPTX with LibreOffice before online editing to avoid ONLYOFFICE parser failures.

Safety / Secret Handling

• Removes real default API keys from vendored PresentAgent config defaults.
• Stops putting internal API keys into ONLYOFFICE document/callback URLs.
• Validates ONLYOFFICE download/callback requests by document key and session context instead of exposing the
  internal workflow key in the URL.

Deployment Notes

• ONLYOFFICE remains optional.
• Local development expects:
  • ONLYOFFICE_DOCUMENT_SERVER_URL=/onlyoffice
  • ONLYOFFICE_THINKFLOW_PUBLIC_URL=...
  • ONLYOFFICE_DOCUMENT_DOWNLOAD_BASE_URL=...
  • storage.externalHost=http://localhost:3003/onlyoffice inside the Document Server container
• Production should place ONLYOFFICE behind a trusted HTTP(S) origin and enable JWT if required.

Validation

• python -m pytest -q tests/test_editable_ppt_service.py tests/test_output_v2_editable_ppt.py
• python -m pytest -q tests/test_online_editor_frame_static.py
• cd frontend_zh && npm run build

Notes

This branch intentionally keeps the new editable PPT workflow and the flashcard UI refresh together because both
land in the ThinkFlow workspace and share the same release surface.