Pairs with node-26 feat/sdr-pins. NodeRecord gains sdr_pins
(service -> serial), sdr_devices and op25_sdr_serial, mirrored from the
node's checkin. PATCH /nodes/{id} validates pins (known services, one
dongle per service) and sends priority/pins as a 'set_sdr_config'
command, never a config re-push. The node restarts OP25 only when OP25's
own dongle changes. The node page's section becomes 'SDRs' with an OP25
SDR dropdown ('Automatic (first SDR)' + detected dongles) and a
per-service dongle dropdown ('Any spare SDR'), plus duplicate-serial and
double-pin warnings.
Verified: c2-core pytest 490 passed; frontend tsc --noEmit clean.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
