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

docs: update agent node mesh features with mobile UI and hardware caps

feat(mesh): implement Phase 6 Rich Health Metrics ...

- Enhanced agent-node to collect per-core CPU, frequency, available RAM, and load avg.
- Updated gRPC server to ingest and propagate rich health metrics via heartbeats.
- Updated Pydantic schemas to expose rich metrics in REST and WebSocket snapshots.
- Fixed UI tooltips in NodesPage.js to pop downwards and show detailed statistics.
- Fixed RegistrationResponse field mismatch (message -> error_message).
- Updated feature documentation for Agent Node Mesh.

Fix Nodes UI WebSocket and metrics, add feature documentation