* fix: sync pasted/uploaded images across collaborating tabs
- Implement file delta synchronization to broadcast image file data
- Add periodic file sync check to catch async file data arrival
- Wrap Excalidraw addFiles API to automatically emit file changes
- Enhance socket element-update to include file payloads
- Add comprehensive E2E test for image collaboration scenarios
- Improve CORS flexibility for development localhost ports
Fixes#25: New images not appearing when collaborating - collaborators
now see uploaded images immediately instead of placeholder until refresh.
* perf: increase file sync polling interval from 500ms to 1000ms
Reduces CPU overhead while still catching async file arrivals. Most
updates go through the addFiles wrapper anyway.
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Co-authored-by: Zimeng Xiong <zxzimeng@gmail.com>
Zimeng Xiong