hub: default to kiosk mode (empty api_key) for the closed LAN

The SPA doesn't send X-API-Key, so a non-empty api_key made the dashboard
401 and show no cameras. Default api_key to "" (no auth) for the closed
travel-router network, consistent with anonymous MQTT. Document the kiosk
decision, the GoPro Hero 3 protocol, and the gotcha that the pull updater
deploys only the binary (config.yaml must be changed on the Pi).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CONTEXT.md

@@ -183,6 +183,16 @@ reach; the Pi pulls instead.
     status/heartbeat (numeric `millis()`) — the hub ignores it / stamps server-side.
 14. **Legacy id migration:** `handleAnnounce` migrates a MAC registered under a
     different `camera_id` (e.g. a pre-self-id `cam-NNN`) to the node's self-id.
+15. **Kiosk API auth:** `api_key: ""` in `config.yaml` = no auth on `/api/v1/*`
+    (closed LAN, consistent with anonymous MQTT). A non-empty key requires the SPA
+    to send `X-API-Key` too, or the dashboard 401s and shows no cameras.
+16. **Ops gotcha:** the pull updater swaps only the **binary**. `config.yaml` is NOT
+    auto-deployed — change it on the Pi (`/opt/remoterig/config.yaml` + restart).
+17. **GoPro Hero 3 protocol** (validated on a Silver): API host `10.5.5.9`, status
+    read `GET /camera/se?t=<pwd>` (binary, starts with 0x00 — read the stream, not
+    Arduino String), recording = byte 29, battery = byte 19; record start/stop =
+    `/bacpac/SH?t=<pwd>&p=%01/%00`. ESP-01S flashing needs RST tied HIGH (RST→GND
+    holds it in reset) and a known-good UART adapter (verify with a TX↔RX loopback).
 
 ## 10. Conventions