Prevent render conficts (hopefully)

src/activities/home/HomeActivity.h

@@ -44,4 +44,5 @@ class HomeActivity final : public Activity {
   void onExit() override;
   void loop() override;
   void render(RenderLock&&) override;
+  bool preventAutoSleep() override { return !firstRenderDone || recentsLoading || !recentsLoaded; }
 };

src/main.cpp

@@ -135,6 +135,10 @@ void enterDeepSleep() {
 
   activityManager.goToSleep();
 
+  // Keep the render mutex until the CPU enters deep sleep so any previously queued
+  // render task cannot race the synchronous sleep-screen transition.
+  RenderLock renderLock;
+
   display.deepSleep();
   LOG_DBG("MAIN", "Entering deep sleep (powerBtn isPressed=%d, rawPin=%d)", gpio.isPressed(HalGPIO::BTN_POWER),
           digitalRead(InputManager::POWER_BUTTON_PIN) == LOW);