Phase 0: record host bring-up progress on the car unit

LTE is up over QMI on povo, metered and ranked below Ethernet/WiFi, with
failover tested. CAN interfaces now have stable udev names (can_pcan,
can_onboard) since canN order raced at boot, so references to can1/can0
go. GNSS stays open: gpsd runs but has no fix until an open-sky test,
which is now what blocks the moving map. Kernel-update rebuild steps
are documented for both out-of-tree modules; time sync is pinned to NICT.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -16,7 +16,7 @@ rest down.
 ## Shape
 
 ```
-   CAN (can1) ──▶ can-bridge ──┐
+   CAN         ──▶ can-bridge ──┐
    OBD-II      ──▶ obd-poller ─┤
    GNSS        ──▶ gnss        ├──▶  message bus  ──┬──▶ recorder (disk)
    camera      ──▶ vision*     ─┘                   ├──▶ hud (local video out)