docs: add comprehensive documentation for all components
- Add frontend README with pages, composables, and architecture
- Add runtime README with quick example (docs coming soon)
- Add CLI README with command overview (docs coming soon)
- Update VOD API README with share endpoints
- Mark AppView as work in progress
- Update DESIGN.md with recent decisions (share endpoints, OG images, runner fixes)
- Update main README with correct paths and documentation links
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>