merge upstream/master: logging pragma, screenshot retrieval, nbsp fix

Merge 3 upstream commits into mod/master:
- feat: Allow screenshot retrieval from device (#820)
- feat: Add central logging pragma (#843)
- fix: Account for nbsp character as non-breaking space (#757)

Conflict resolution:
- src/main.cpp: kept mod's HalPowerManager + upstream's Logging/screenshot
- SleepActivity.cpp: kept mod's letterbox fill rework, applied LOG_* pattern

Additional changes for logging compatibility:
- Converted remaining Serial.printf calls in mod files to LOG_* macros
  (HalPowerManager, BookSettings, BookmarkStore, GfxRenderer)
- Added ENABLE_SERIAL_LOG and LOG_LEVEL=2 to [env:mod] build flags

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/hal/HalPowerManager.cpp

@@ -1,5 +1,6 @@
 #include "HalPowerManager.h"
 
+#include <Logging.h>
 #include <esp_sleep.h>
 
 #include "HalGPIO.h"
@@ -14,16 +15,16 @@ void HalPowerManager::setPowerSaving(bool enabled) {
     return;  // invalid state
   }
   if (enabled && !isLowPower) {
-    Serial.printf("[%lu] [PWR] Going to low-power mode\n", millis());
+    LOG_DBG("PWR", "Going to low-power mode");
     if (!setCpuFrequencyMhz(LOW_POWER_FREQ)) {
-      Serial.printf("[%lu] [PWR] Failed to set low-power CPU frequency\n", millis());
+      LOG_ERR("PWR", "Failed to set low-power CPU frequency");
       return;
     }
   }
   if (!enabled && isLowPower) {
-    Serial.printf("[%lu] [PWR] Restoring normal CPU frequency\n", millis());
+    LOG_DBG("PWR", "Restoring normal CPU frequency");
     if (!setCpuFrequencyMhz(normalFreq)) {
-      Serial.printf("[%lu] [PWR] Failed to restore normal CPU frequency\n", millis());
+      LOG_ERR("PWR", "Failed to restore normal CPU frequency");
       return;
     }
   }