feat(ui-lvgl): quick panel from the status bar; L2 fixes from rc1

The quick panel, as a phone's: pulled down from the status bar (or a tap
on it). Bluetooth, WiFi, GPS, sound, trail and live share switch at a
tap; Advert opens the advert popup (moved here from the Nodes header);
Lock locks the screen; a brightness slider. Holding a tile opens its
settings. Lock and sun glyphs added to the fonts.

Fixes from rc1 testing on the L2:
- GPS status icon: none when GPS is off (the module kept its last fix
  valid, so it stayed green); grey on, green with a fix. ensureGps()
  turns GPS on before trusting that stale fix.
- Screen wake: the panel wakes dark, a frame is drawn, then the
  backlight fades in -- no white flash. Off fades out first.
- Power off / flat battery: the chip wakes every 30 s to look for USB
  power and starts when plugged in (it slept with no wake source before,
  until the reset button). Plugged in when switched off: stays off until
  re-plugged.
- Message ages in a conversation refresh every 2 s, as on ui-new; the
  message popup keeps its age, repeaters heard and delivery up to date.

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

variants/wio-tracker-l2/WioTrackerL2Display.h

@@ -188,6 +188,20 @@ public:
 
 class WioTrackerL2Display : public LGFXDisplay {
   LGFX_WioTrackerL2 disp;
+
+  // The backlight from one PWM level to another over ~180 ms, on a square
+  // curve (the eye sees the low end's steps). Blocks; 0 ends in standby.
+  void fade(uint8_t from, uint8_t to) {
+    const int STEPS = 12;
+    for (int i = 1; i <= STEPS; i++) {
+      const int t = i * 256 / STEPS;   // 0..256
+      const int k = from < to ? t * t / 256 : 256 - (256 - t) * (256 - t) / 256;
+      const int v = from + ((int)to - from) * k / 256;
+      display->panel()->setBrightness((uint8_t)(i == STEPS ? to : (v < 1 ? 1 : v)));
+      delay(15);
+    }
+  }
+
 public:
   WioTrackerL2Display() : LGFXDisplay(320, 240, disp) {}
 
@@ -197,6 +211,26 @@ public:
     display->setBrightness(PWM[level > 4 ? 4 : level]);
   }
 
+  // Screen off: the backlight fades out, then the panel sleeps. Screen on: the
+  // panel wakes with the light still off -- the caller draws a fresh frame
+  // first (the panel shows what's left in its memory for a moment, a white
+  // flash) -- and fadeIn() brings the light up.
+  void turnOff() override {
+    if (_isOn) {
+      fade(display->getBrightness(), 0);
+      display->sleep();
+    }
+    _isOn = false;
+  }
+  void turnOn() override {
+    if (!_isOn) {
+      display->panel()->setSleep(false);
+      delay(10);   // the panel takes no pixels just out of sleep
+    }
+    _isOn = true;
+  }
+  void fadeIn() { fade(0, display->getBrightness()); }
+
   // direct access to the LGFX device (LVGL flush/touch glue)
   lgfx::LGFX_Device* lgfxDevice() { return &disp; }
   Panel_WioTrackerL2& panel() { return disp.panelL2(); }