feat(mesh): robust node connectivity and sync reliability fixes ...

- Fixed Node Registry persistence by adding missing db.commit() for online/offline status updates.
- Resolved 'Seed from Local' sync failures by correctly tracking mesh memberships in the TaskAssistant service.
- Enhanced frontend safety: disabled offline node selection and filtered source node candidates.
- Added 'Receiver Only' toggle for more granular control over multi-node synchronization.
- Corrected false-positive 'Source Node Disconnected' alert by verifying global connection status.
- Improved logging in Hub and Agent Nodes for better debugging of file transfer events.

docs: remove legacy component refs and generalize chat interface

docs: add coding assistant ui design philosophy and layout reference