perf(ui-lvgl): lower clock when idle, fewer redraws, wake on BLE frames

- CPU at 80 MHz with the screen on after 2 s without touch or animation;
  a touch restores the full clock before its frame is drawn
- setText(): periodic refreshes no longer redraw unchanged labels
  (status bar, Home, lock, Diag, GPS, compass, clock, map, nav, nearby)
- map markers kept across the 3 s rebuild when unchanged
- app connected: the loop blocks until a BLE frame arrives
  (serialFrameArrived / hasPendingFrames) instead of polling every 2 ms
- PSRAM: boot frame sprite and the HTTP response buffer released

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

src/helpers/BaseSerialInterface.h

@@ -25,6 +25,10 @@ public:
   // isConnected() so single-transport interfaces are unchanged.
   virtual bool isClientConnected() const { return isConnected(); }
 
+  // For a loop that sleeps between passes: frames waiting to be read or sent.
+  // An interface that can't tell says true (poll it often).
+  virtual bool hasPendingFrames() const { return true; }
+
   virtual bool isWriteBusy() const = 0;
   virtual size_t writeFrame(const uint8_t src[], size_t len) = 0;
   virtual size_t checkRecvFrame(uint8_t dest[]) = 0;

src/helpers/esp32/DualSerialInterface.h

@@ -52,6 +52,11 @@ public:
   bool isClientConnected() const override { return isBLEConnected(); }
 #endif
 
+  // USB can't tell without reading it.
+  bool hasPendingFrames() const override {
+    return (_ble_enabled && _ble.isConnected()) ? _ble.hasPendingFrames() : true;
+  }
+
   bool isWriteBusy() const override {
     return (_ble_enabled && _ble.isConnected()) ? _ble.isWriteBusy() : _usb.isWriteBusy();
   }

src/helpers/esp32/SerialBLEInterface.cpp

@@ -10,6 +10,8 @@
 
 #define ADVERT_RESTART_DELAY  1000   // millis
 
+__attribute__((weak)) void serialFrameArrived() {}
+
 // As the nRF52 interface: 20-30 ms for the first 30 s (the app finds it at
 // once), then 152.5 ms. Left alone, the library advertises every 30-60 ms
 // for as long as nothing is connected. Units of 0.625 ms.
@@ -187,6 +189,7 @@ void SerialBLEInterface::onWrite(BLECharacteristic* pCharacteristic, esp_ble_gat
     if (xQueueSend(recv_queue, &frame, 0) != pdTRUE) {
       BLE_DEBUG_PRINTLN("ERROR: onWrite(), recv_queue is full!");
     }
+    serialFrameArrived();
   }
 }
 

src/helpers/esp32/SerialBLEInterface.h

@@ -8,6 +8,10 @@
 #include <freertos/FreeRTOS.h>
 #include <freertos/queue.h>
 
+// A frame from the app was queued (the BLE stack's task). Weak, empty by
+// default: a firmware whose loop blocks between passes defines it to wake it.
+void serialFrameArrived();
+
 class SerialBLEInterface : public BaseSerialInterface, BLESecurityCallbacks, BLEServerCallbacks, BLECharacteristicCallbacks {
   BLEServer *pServer;
   BLEService *pService;
@@ -102,6 +106,7 @@ public:
 
   bool isConnected() const override;
 
+  bool hasPendingFrames() const override { return send_queue_len > 0 || uxQueueMessagesWaiting(recv_queue) > 0; }
   bool isWriteBusy() const override;
   size_t writeFrame(const uint8_t src[], size_t len) override;
   size_t checkRecvFrame(uint8_t dest[]) override;