fix: prevent idle freeze by hardening NTP and clock power management

BootNtpSync now acquires a HalPowerManager::Lock for the entire WiFi/NTP
task lifecycle, keeping the CPU at full speed during scan, connect, sync,
and teardown. The clock refresh logic in the main loop now explicitly
restores CPU frequency and resets the activity timer before requesting a
render, preventing display SPI operations from running at 10 MHz.

Made-with: Cursor

src/main.cpp

@@ -416,9 +416,13 @@ void loop() {
       if (lastRenderedMinute < 0) {
         lastRenderedMinute = currentMinute;
         if (sawInvalidTime) {
+          lastActivityTime = millis();
+          powerManager.setPowerSaving(false);
           activityManager.requestUpdate();
         }
       } else if (currentMinute != lastRenderedMinute) {
+        lastActivityTime = millis();
+        powerManager.setPowerSaving(false);
         activityManager.requestUpdate();
         lastRenderedMinute = currentMinute;
       }