feat(ui): CardKB (I2C keyboard) support with full keyboard-only navigation

Auto-detected at boot on Wire1/Grove (addr 0x5F) -- no setting to flip, and a
no-op on boards without that bus or with nothing attached. This UI's key
codes (KEY_LEFT/UP/DOWN/RIGHT/ENTER/CANCEL) already match CardKB's own byte
protocol, so most input needs zero translation and flows through the same
key queue as physical buttons.

Two bytes get remapped in UITask::pollCardKB():
- Enter, only when the on-screen keyboard's plain grid state is active (no
  placeholder/accent popup, not in cursor-mode), becomes a new KEY_KB_ENTER
  sentinel meaning "submit the field" -- reusing plain KEY_ENTER there would
  insert a stray character, since a CardKB typist's row/col never reflect an
  intentional grid selection. Everywhere else Enter is untouched, so
  selecting a placeholder or committing an accent still works normally.
- Tab (otherwise unused) becomes KEY_CONTEXT_MENU, standing in for the
  "Hold-Enter" long-press gesture CardKB has no way to produce -- without it,
  ~30 context menus across the UI (message reply/navigate, Bot/Admin/
  Repeater, ...) would be unreachable from the keyboard alone.

KeyboardWidget gains a direct-typing path: printable ASCII inserts straight
at the cursor bypassing the grid, Backspace deletes, KEY_KB_ENTER submits.

Build-verified: WioTrackerL1_companion_solo_dual and
WioTrackerL1Eink_companion_solo_dual both compile and link clean; also
smoke-tested Heltec_mesh_solar_companion_radio_ble (no ENV_PIN_SDA/SCL) to
confirm zero regression on boards without the feature.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

examples/companion_radio/ui-new/UITask.h

@@ -193,6 +193,17 @@ class UITask : public AbstractUITask {
   void enqueueKey(char c);
   bool dequeueKey(char& c);
 
+  // Optional M5Stack CardKB (I2C keyboard, addr 0x5F) on the Grove/Wire1 bus
+  // -- reuses ENV_PIN_SDA/ENV_PIN_SCL (already brought up for
+  // EnvironmentSensorManager) as the "this board has a second I2C bus" gate,
+  // rather than a new board-specific pin define. No-op entirely on boards
+  // without that bus, or when nothing ACKs 0x5F at boot.
+#if defined(ENV_PIN_SDA) && defined(ENV_PIN_SCL)
+  bool     _has_cardkb = false;
+  uint32_t _cardkb_poll_ms = 0;
+#endif
+  void pollCardKB();
+
   void setCurrScreen(UIScreen* c);
 
   // Centred alert overlay (the showAlert() box). Wraps long text to up to