Add 12-OBD-Speed: ELM327 speed over BLE on a GIF background

- speed page: 120 px antialiased number (lv_font_conv) + 0-200 km/h arc
  gauge over ezgif-5-cb56986bc7.gif (embedded via board_build.embed_files)
- swipe-left menu: scan, OBD-like adapters first, tap to select; adapter
  remembered in NVS, auto-connect at boot and reconnect every 3 s
- ELM327 init ATZ/ATE0/ATL0/ATS0/ATH0/ATSP0/0100, then 010D polling
- shared ini: -DLV_LVGL_H_INCLUDE_SIMPLE for generated fonts

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

CLAUDE.md

@@ -79,6 +79,7 @@ Display color format is `RGB565_SWAPPED` (ST77916 byte order, set in `lv_conf.h`
 | `1-Instructions` | Spec PDF (duplicate), AIDA64 remote-sensor layout `aida_remote_1.85.rslcd`, MJPEG conversion tool (Windows .NET, converts video to 360×360 MJPEG 25 fps) |
 | `2-Program Example/Demo_Arduino` | **Vendor only:** `library/` (3 libs), `lv_conf.h` (vendor original), `sd/` (SD listing example; its lv_conf.h has FATFS edits), `docs/` (setup screenshots + compile instructions). The vendor's original LVGL demo sketch no longer exists unmodified. |
 | `shared` | **Shared code for all JC3636W518 projects:** `jc3636w518.ini` (PlatformIO base config), `include/lv_conf.h` (LVGL 9.6), `lib/JC3636W518` (board library). See its `README.md` |
+| `12-OBD-Speed` | **The new program (in progress):** speed from the ELM327 over BLE as big number + arc gauge on a GIF background; swipe left for the adapter menu (scan, select → remembered in NVS, auto-reconnect every 3 s). See its `README.md` |
 | `11-BLE-Scanner` | **BLE scanner with on-screen UI** (NimBLE-Arduino 2.5.1): live device list, tap to list services/characteristics, ELM327 test (ATZ/ATE0/ATI/ATRV/0100). Results saved to LittleFS `/ble_log.txt`; serial `d` dump, `c` clear, `s` device list. See its `README.md` |
 | `10-OBD-Display-2024` | **Leftovers of the 2024 OBD project:** `display_gif_embedded`, `display_gif_sd`, `assets/gifs`, `_archive/lvgl9_broken` (bridge/ELMulator/WiFi speed sketch removed 2026-10-23) |
 | `3-Specification` | Spec sheet (factory firmware features, interface photo) |
@@ -121,3 +122,7 @@ AliExpress "ELM327 Mini V2.1 Bluetooth OBD **Dual Mode** 5.1" — dual mode = Bl
 - Draw buffer is in internal RAM; PSRAM is available for larger buffers / images.
 - **LittleFS** works on the `spiffs` partition of `huge_app.csv` (~900 KB); the first mount after flashing formats it (prints `Corrupted dir pair` / `mount failed (-84)` and some `task_wdt ... task not found` once — harmless).
 - BLE (NimBLE) in the user's home: ~12 devices visible within 10 s.
+- Big fonts: generate with `npx lv_font_conv` (Node 22 installed) from `lvgl/scripts/generators/built_in_font/Montserrat-Medium.ttf`; `-DLV_LVGL_H_INCLUDE_SIMPLE` (in shared ini) makes the generated `#include` work.
+- Binary assets (GIFs): `board_build.embed_files = data/x.gif` → `extern const uint8_t x_start[] asm("_binary_data_x_gif_start")` (no huge C arrays).
+- Serial output right after a reset can be lost/garbled (USB-CDC re-enumeration, prints from two cores interleave) — don't conclude a task isn't running from a missing early line.
+- `Preferences` prints `nvs_open failed: NOT_FOUND` the first time a namespace is read before it was written — harmless.