feat(ui): optional magnetic flip-cover screen lock via user-wired Hall sensor

No board in this repo has one built in, and no default pin is assumed
anywhere -- whoever wires a Hall-effect or reed sensor to a free GPIO sets
PIN_HALL_SENSOR (and HALL_ACTIVE_HIGH, for a sensor that pulls the pin high
rather than low on presence) as a build_flag on their own env. Entirely
opt-in and a no-op elsewhere, same pattern as PIN_GPIO1..4/ADC_MULTIPLIER/
CARDKB_ENABLE.

Level-triggered polling (like pollCardKB()) rather than an edge interrupt --
a magnet held near the sensor reads the same way every tick, so the new
pollHallSensor() only acts on the two transitions. Closing locks and blanks
the display with no wake grace (the cover is physically over the screen, so
there's nothing to show); opening unlocks and wakes it, with no key combo
either way. Both are independent of the Auto-lock setting, which is a
timeout, not a physical event.

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

examples/companion_radio/ui-new/UITask.cpp

@@ -1404,6 +1404,17 @@ void UITask::begin(DisplayDriver* display, SensorManager* sensors, NodePrefs* no
   _has_cardkb = (Wire1.endTransmission() == 0);
 #endif
 
+#if defined(PIN_HALL_SENSOR)
+  // Internal pull matches the default polarity: pulled up so an active-low
+  // sensor reads HIGH at rest, pulled down so an active-high one reads LOW at
+  // rest. Most reed/Hall breakouts are open-drain, active-low -- HALL_ACTIVE_HIGH
+  // is only for modules wired the other way.
+  pinMode(PIN_HALL_SENSOR, HALL_ACTIVE_HIGH ? INPUT_PULLDOWN : INPUT_PULLUP);
+  _hall_magnet_present = HALL_ACTIVE_HIGH ? (digitalRead(PIN_HALL_SENSOR) == HIGH)
+                                           : (digitalRead(PIN_HALL_SENSOR) == LOW);
+  if (_hall_magnet_present) _locked = true;   // booting with the cover already closed
+#endif
+
 #if defined(PIN_USER_BTN)
   user_btn.begin();
 #endif
@@ -2237,6 +2248,37 @@ void UITask::pollCardKB() {
 #endif
 }
 
+// Level-triggered, like pollCardKB() -- a magnet held near the sensor reads the
+// same way every tick, so this only acts on the two edges (closed/opened), not
+// on every poll. Fully autonomous: closing locks and blanks the display
+// immediately (no wake grace -- the cover is physically over the screen, so
+// there's nothing to show), opening unlocks and wakes it, with no combo or
+// keypress either way. Independent of Auto-lock (Settings > Display), which is
+// a timeout-driven setting -- this is a direct physical event.
+void UITask::pollHallSensor() {
+#if defined(PIN_HALL_SENSOR)
+  bool present = HALL_ACTIVE_HIGH ? (digitalRead(PIN_HALL_SENSOR) == HIGH)
+                                   : (digitalRead(PIN_HALL_SENSOR) == LOW);
+  if (present == _hall_magnet_present) return;
+  _hall_magnet_present = present;
+
+  if (present) {   // cover closed
+    _locked = true;
+    _lock_wake_until = 0;
+    if (_display) _display->turnOff();
+#ifdef PIN_LED
+    digitalWrite(PIN_LED, LOW);   // same as the auto-off path -- one less thing lit under a closed cover
+#endif
+  } else {   // cover opened
+    _locked = false;
+    if (_display && !_display->isOn()) _display->turnOn();
+    uint32_t aoff = autoOffMillis();
+    if (aoff > 0) _auto_off = millis() + aoff;
+  }
+  _next_refresh = 0;
+#endif
+}
+
 void UITask::loop() {
   // Background delivery: resend pending on-device DMs whose ACK timed out, and
   // finalise the ✗ marker — runs regardless of which screen is active.
@@ -2335,6 +2377,7 @@ void UITask::loop() {
   }
 #endif
   pollCardKB();
+  pollHallSensor();
 #ifdef ENV_USE_TCA8418
   {
     extern char tca8418_keypad_read();   // provided by the active variant

examples/companion_radio/ui-new/UITask.h

@@ -208,6 +208,20 @@ class UITask : public AbstractUITask {
 #endif
   void pollCardKB();
 
+  // Optional magnetic "flip cover" lock: a Hall-effect or reed sensor wired to
+  // any free GPIO, closing (pulling active) when a magnet is near. Entirely
+  // user-supplied -- no board in this repo ships one, so PIN_HALL_SENSOR must
+  // be added as a build_flag by whoever wires the sensor up; no-op everywhere
+  // else. HALL_ACTIVE_HIGH overrides the default polarity for modules that
+  // pull the pin HIGH (instead of LOW) when the magnet is present.
+#if defined(PIN_HALL_SENSOR)
+#ifndef HALL_ACTIVE_HIGH
+  #define HALL_ACTIVE_HIGH 0
+#endif
+  bool _hall_magnet_present = false;
+#endif
+  void pollHallSensor();
+
   void setCurrScreen(UIScreen* c);
 
   // Centred alert overlay (the showAlert() box). Wraps long text to up to