Add touch tap gesture for back navigation

Implements a reusable touch tap gesture in the top-left corner that maps to the Back button. The gesture is automatically integrated into wasPressed/wasReleased for Back button, making it available across all screens without per-activity code. Also fixes low-power CPU frequency floor to 80 MHz on PSRAM boards to prevent SD write and PSRAM instability caused by APB clock dropping below safe threshold.

lib/hal/HalGPIO.cpp

@@ -231,6 +231,8 @@ unsigned long HalGPIO::getHeldTime() const { return inputMgr.getHeldTime(); }
 
 unsigned long HalGPIO::getPowerButtonHeldTime() const { return inputMgr.getPowerButtonHeldTime(); }
 
+bool HalGPIO::wasTouchTap(float& nx, float& ny) const { return inputMgr.wasTouchTap(nx, ny); }
+
 void HalGPIO::startDeepSleep() {
   // Ensure that the power button has been released to avoid immediately turning back on if you're holding it
   while (inputMgr.isPressed(BTN_POWER)) {

lib/hal/HalGPIO.h

@@ -72,6 +72,11 @@ class HalGPIO {
   unsigned long getHeldTime() const;
   unsigned long getPowerButtonHeldTime() const;
 
+  // Touch: one-shot tap with the release position normalized 0..1 in the panel's
+  // native orientation. Returns false on non-touch devices. (Reusable gesture
+  // primitive; see MappedInputManager for the top-left = Back mapping.)
+  bool wasTouchTap(float& nx, float& ny) const;
+
   // Setup wake up GPIO and enter deep sleep
   void startDeepSleep();
 

lib/hal/HalPowerManager.h

@@ -28,7 +28,16 @@ class HalPowerManager {
   SemaphoreHandle_t modeMutex = nullptr;  // Protect access to currentLockMode
 
  public:
-  static constexpr int LOW_POWER_FREQ = 10;                    // MHz
+  // On PSRAM boards (classic ESP32 / M5Paper) the APB clock follows the CPU below
+  // 80 MHz, and APB clocks both the SD SPI bus and the 80 MHz PSRAM (which holds
+  // the framebuffer). Dropping to 10 MHz breaks SD writes and PSRAM, so floor the
+  // low-power CPU at 80 MHz (APB stays pinned at 80 for CPU 80/160/240, so power
+  // still drops from the 240 MHz default while SD/PSRAM stay stable).
+#if defined(BOARD_HAS_PSRAM)
+  static constexpr int LOW_POWER_FREQ = 80;  // MHz (APB-safe floor for PSRAM/SD)
+#else
+  static constexpr int LOW_POWER_FREQ = 10;  // MHz
+#endif
   static constexpr unsigned long IDLE_POWER_SAVING_MS = 3000;  // ms
   static constexpr unsigned long BATTERY_POLL_MS = 1500;       // ms
 

src/MappedInputManager.cpp

@@ -54,9 +54,29 @@ bool MappedInputManager::mapButton(const Button button, bool (HalGPIO::*fn)(uint
   return false;
 }
 
-bool MappedInputManager::wasPressed(const Button button) const { return mapButton(button, &HalGPIO::wasPressed); }
+// Top-left corner of the panel (panel-native, normalized). Generous so it's easy
+// to hit; v1 is not yet orientation-mapped (see wasBackGesture NOTE in header).
+static constexpr float BACK_GESTURE_FRAC_X = 0.22f;
+static constexpr float BACK_GESTURE_FRAC_Y = 0.12f;
 
-bool MappedInputManager::wasReleased(const Button button) const { return mapButton(button, &HalGPIO::wasReleased); }
+bool MappedInputManager::wasBackGesture() const {
+  float nx = 0.0f, ny = 0.0f;
+  if (!gpio.wasTouchTap(nx, ny)) return false;
+  return nx <= BACK_GESTURE_FRAC_X && ny <= BACK_GESTURE_FRAC_Y;
+}
+
+bool MappedInputManager::wasPressed(const Button button) const {
+  // A top-left tap fires on the release frame; expose it on Back's press edge too
+  // so menus that act on wasPressed(Back) also respond. Deliberately NOT folded
+  // into isPressed, so a quick tap never satisfies the readers' long-press-home.
+  if (button == Button::Back && wasBackGesture()) return true;
+  return mapButton(button, &HalGPIO::wasPressed);
+}
+
+bool MappedInputManager::wasReleased(const Button button) const {
+  if (button == Button::Back && wasBackGesture()) return true;
+  return mapButton(button, &HalGPIO::wasReleased);
+}
 
 bool MappedInputManager::isPressed(const Button button) const { return mapButton(button, &HalGPIO::isPressed); }
 

src/MappedInputManager.h

@@ -19,6 +19,11 @@ class MappedInputManager {
   bool wasPressed(Button button) const;
   bool wasReleased(Button button) const;
   bool isPressed(Button button) const;
+  // Reusable touch "back" gesture: a tap released in the top-left corner. Folded
+  // into Back's press/release edges, so every screen gets it with no per-activity
+  // code and no coordinates passed. False on non-touch devices.
+  // NOTE: v1 uses panel-native coordinates (not yet orientation-mapped).
+  bool wasBackGesture() const;
   bool wasAnyPressed() const;
   bool wasAnyReleased() const;
   unsigned long getHeldTime() const;