feat: FEAT-14 dual T3U — wlan2 uplink, wlan1 AP, onboard wlan0 fallback

PLAN.md

@@ -12,14 +12,13 @@ pick up the project without needing prior chat history.
 - **Board**: Raspberry Pi 3 Model B Rev 1.2, 906MB RAM. Confirmed too weak to run an AI coding
   agent — all agent-assisted dev work happens on a separate local machine; the Pi is only used
   for hardware bring-up/testing/deployment via SSH (`yaris@<pi-ip>`).
-- **WiFi**: Dual-radio setup — **TP-Link Archer T3U (RTL8812BU)** USB dongle as `wlan1` and the
-  onboard BCM43438 as `wlan0`. **2026-08-12 role swap**: the fast T3U now hosts the in-car AP
-  ("vroom vroom yaris de course" on 5GHz at 10.42.0.1) for fast phone access (Android dev, video
-  browsing); the weak onboard radio carries the internet uplink (home WiFi "BuzzBis" +
-  phone hotspot, static IP 192.168.50.220, gw 192.168.50.1). Both radios active simultaneously.
-  Tradeoff: away-from-home uploads (dashcam/trip sync) now run over the weak onboard radio — a
-  background task, accepted by owner. A single radio cannot be AP + client at once, so the
-  phone-hotspot uplink cannot also live on wlan1 while it hosts the AP.
+- **WiFi**: **Dual T3U** setup (2026-08-14, FEAT-14) — two TP-Link Archer T3U (RTL8812BU)
+  dongles: `wlan1` hosts the in-car AP ("vroom vroom yaris de course" on 5GHz at 10.42.0.1)
+  and `wlan2` carries the internet uplink (home WiFi "BuzzBis" + phone hotspot, static IP
+  192.168.50.220, gw 192.168.50.1). The onboard BCM43438 (`wlan0`) is retired to a weak
+  fallback. Away-from-home uploads (dashcam/trip sync) now run on a fast AC radio. A single
+  radio cannot be AP + client at once, so the phone-hotspot uplink cannot live on wlan1 while
+  it hosts the AP.
 - **GPS/GSM**: Waveshare **SIM868 GSM/GPRS/GNSS/Bluetooth HAT**. GNSS provides live GPS fixes
   (confirmed working, ~7 satellites, ~80s cold-start TTFF). GSM/GPRS cellular is **not in use**
   (no SIM card available); a Huawei **E3372h-153 4G LTE modem** has been purchased as a future