v2 firmware: HA command channel, battery screen, dynamic Home buttons, tilt-dimmer

Watch-side features developed on the AMOLED-2.06 and shared across all boards:

- BLE command channel (…0005, notify watch→PC) via ble_send_command(); the
  watch stays "dumb" and the daemon maps commands to Home Assistant.
- Battery detail screen + protective low-voltage cutoff; power HAL gains
  battery_mv() / shutdown(), with battery_est.{h,cpp} for the time-left anchor.
- Home screen: dynamic 2-column button grid driven by the desktop config
  (RX "btns" labels); tap notifies {"cmd":"btn","i":N}.
- Dimmer screen: IMU tilt-joystick over the light's brightness / color temp.
  imu_hal_read_accel() added to the HAL (real on 2.06/2.16, no-op elsewhere);
  streams absolute {"cmd":"bri"|"ct","v":..}; daemon seeds the dial via "dim".
  Per-board tilt axis is calibrated with the DIM_CALIB overlay (off by default).

Multi-board fix: enable LV_FONT_MONTSERRAT_20/28 on the 2.16, 1.8 and C6 envs.
Shared ui.cpp uses these glyphs for the launcher tiles and back chevron, so
those three boards had failed to compile since the Phase-2 UI landed. All four
envs now build clean. README: correct the Windows pairing name to "Clawdmeter".

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

firmware/platformio.ini

@@ -42,6 +42,11 @@ build_flags =
     -DLV_USE_ANIMIMG=0
     -DLV_TICK_CUSTOM=1
     -DLV_USE_SNAPSHOT=1
+    ; Montserrat carries the LVGL symbol glyphs (FontAwesome subset) used for the
+    ; v2 launcher tile icons and the back chevron. The brand Styrene/Tiempos fonts
+    ; are Latin-only and have no symbols. Shared ui.cpp needs these on every board.
+    -DLV_FONT_MONTSERRAT_20=1
+    -DLV_FONT_MONTSERRAT_28=1
 
 lib_deps =
     moononournation/GFX Library for Arduino@^1.5.6
@@ -99,6 +104,11 @@ build_flags =
     -DLV_USE_ANIMIMG=0
     -DLV_TICK_CUSTOM=1
     -DLV_USE_SNAPSHOT=1
+    ; Montserrat carries the LVGL symbol glyphs (FontAwesome subset) used for the
+    ; v2 launcher tile icons and the back chevron. The brand Styrene/Tiempos fonts
+    ; are Latin-only and have no symbols. Shared ui.cpp needs these on every board.
+    -DLV_FONT_MONTSERRAT_20=1
+    -DLV_FONT_MONTSERRAT_28=1
 
 lib_deps =
     ; 1.6.4+ ships Arduino_SH8601 in mainline
@@ -230,6 +240,11 @@ build_flags =
     ; 480×480) which doesn't fit in C6 internal SRAM. send_screenshot
     ; prints SCREENSHOT_UNSUPPORTED on this board.
     -DLV_USE_SNAPSHOT=0
+    ; Montserrat carries the LVGL symbol glyphs (FontAwesome subset) used for the
+    ; v2 launcher tile icons and the back chevron. The brand Styrene/Tiempos fonts
+    ; are Latin-only and have no symbols. Shared ui.cpp needs these on every board.
+    -DLV_FONT_MONTSERRAT_20=1
+    -DLV_FONT_MONTSERRAT_28=1
 
 lib_deps =
     ; this board uses the CO5300 (same controller as the S3 2.16); Arduino_CO5300