12-OBD-Speed: battery voltage arc and idle/screen-off mode

- ATRV every 2 s; voltage arc in the bottom gap (11-15 V) + number,
  colored by state (low / weak / resting / charging / overcharge)
- idle after Off/2/5/10 min without speed data (settings page, NVS):
  screen off, GIF paused, OBD polling stopped, ATRV every 30 s;
  wakes on touch (swallowed by a top-layer overlay) or > 13.2 V
- status pill moved up to make room for the voltage

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

12-OBD-Speed/README.md

@@ -5,11 +5,17 @@ Uses the shared board library and LVGL 9.6 (`../shared`), NimBLE-Arduino 2.5.1.
 
 ## Use
 - **Speed page** — speed in km/h (`--` = no data: not connected, or ignition off), arc gauge 0–200 km/h,
-  status at the bottom (adapter name when running, otherwise what it is doing).
+  status pill below the number (adapter name when running, otherwise what it is doing).
+  **Battery voltage** (`ATRV`, every 2 s) as a small arc in the bottom gap (11–15 V) + number; color:
+  red < 11.8 V, orange < 12.2 V, green < 13.0 V (resting OK), blue ≤ 14.8 V (charging), red above (overcharge).
 - **Swipe left → adapter menu** — scans while open. OBD-like adapters (name OBD/ELM/…, or service FFF0/FFE0/18F0)
   are listed first in green. **Tap one** to select it: it is remembered (NVS) and connected immediately.
   **Forget** clears the remembered adapter, **Done** (or swipe right) returns to the speed page.
-- **Swipe left again → settings** — screen rotation 0 / 90 / 180 / 270 degrees (tap to apply; remembered in NVS, applied at boot).
+- **Swipe left again → settings** — screen rotation 0 / 90 / 180 / 270 degrees, and **screen off without data** Off / 2 / 5 / 10 min (default 2). Both remembered in NVS.
+- **Idle** — after that time without speed data (ignition off, adapter gone) the screen goes dark, the GIF pauses and
+  OBD polling stops; only `ATRV` every 30 s (answered by the adapter itself, doesn't wake the car's bus).
+  Wakes on a touch (the touch is swallowed) or by itself when the voltage rises above 13.2 V (engine started).
+  Not used while no adapter is chosen.
 - On power-up the remembered adapter is connected automatically; if the link drops or the adapter is not
   there (car off), it retries every 3 s. With no adapter remembered, the device starts on the menu page.