fix(library): yield the SD card between entries in the dual-core index walk

CHANGELOG.md

@@ -38,6 +38,7 @@
 
 ### Fixed
 
+- On the X4 Pro and Sticky, the Home screen no longer stalls waiting for the SD card while the Library indexes in the background.
 - Small images that are scaled up, such as a short progressive JPEG, are now cached after the first draw instead of being decoded again on every screen refresh.
 - The serial log no longer reports errors for normal events: a missing image, section or dictionary cache file on first open, an outdated section cache being rebuilt, and a device without a clock chip or motion sensor. Log lines that were missing a line break now end cleanly, and SD, display, TLS and frontlight messages use the standard log format.
 - X4 Pro light-sleep firmware shows its real version (for example `1.6.0-x4-pro`) instead of "dev" in Settings, on the boot screen, and in the web and OTA version checks.

src/activities/library/LibraryPrewarm.cpp

@@ -77,6 +77,11 @@ bool serviceBuild(void*) {
     fullSpeed.emplace();
     pausedMs += millis() - pausedAtMs;
   }
+  // Dual-core: give up the card for a tick between entries. The storage mutex
+  // does not hand off to a waiter, so without this the walk on core 0 can
+  // retake it before a Home task waiting on core 1 wakes, starving it for a
+  // whole directory. Single-core runs at idle priority and needs no yield.
+  if (portNUM_PROCESSORS > 1) vTaskDelay(1);
   return !cancelRequested.load(std::memory_order_acquire);
 }