Changes:
- Fix datetime serialization with UTC 'Z' suffix for correct timezone display
- Add PDF upload support with extension fallback for MIME detection
- Fix LOT add/remove by creating new list for SQLAlchemy JSON change detection
- Add file message components (FileMessage, ImageLightbox, UploadPreview)
- Add multi-file upload support with progress tracking
- Link uploaded files to chat messages via message_id
- Include file attachments in AI report generation
- Update specs for file-storage, realtime-messaging, and ai-report-generation
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Co-Authored-By: Claude <noreply@anthropic.com>
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