[Feature] Collaboration & Sharing - Share Projects and Export for Review

[vzeman]

Summary

Implement sharing and lightweight collaboration features that allow users to share their work with stakeholders, collect feedback, and exchange projects with other editors. Collaboration is the final layer of polish that makes the tool usable in professional team contexts.

Requirements

• Export shareable project bundle (assets + config, no API keys)
• Export video with chapter markers for review
• Annotation mode: add timestamped comments/notes to video for review
• Export comment report as PDF
• Share via native OS share sheet
• Generate preview link (local HTTP server for local network sharing)
• Export scene breakdown as PDF or markdown document
• Import feedback annotations from collaborator

Acceptance Criteria

• Project bundle export contains all assets and config but strips all API keys
• Annotation mode allows adding time-stamped comments on any video frame
• Comment report exports to PDF with timestamps and screenshots
• Local HTTP preview server starts and serves the project for LAN access
• Scene breakdown PDF export is legible and professionally formatted
• Feedback annotations import correctly and display in the editor

Related

Part of the ai-video-editor Flutter application. Depends on #61 (Project Management) and #72 (Final Video Export). Final phase feature.