Add POST /api/mesh/test-send (fire a labeled test broadcast on a chosen
mesh+channel via the live transport) and GET /api/meshcore/channels
(surface the companion's enumerated channel names). "Send test message"
cards on both Connection pages, with the MeshCore one listing real
channels. Lets the operator confirm a mesh's send path on demand.
Co-authored-by: Matt Johnson <mj@k7zvx.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
