Adds an explicit SPA-side join section in position-record.md and
references the implementation file (src/data/devices.ts ->
useDevicesByImei) from the deviceId field row in the WS contract page.
Captures the brief drift-and-realign episode where the SPA was keying
by uuid before Phase 3.4 and the device list panel rendered id
prefixes.
The contract itself didn't change - the SPA implementation just caught
up with what the wiki already said.
julian
111a542034