SD card improvements (#214)

- Implement SD card locking logic and helper functions
- Fix issue with running ELF apps from SD card: this would crash when launched from the AppList
- Reduce Boot app wait time to 1 second
- Speed up boot by about 0.1 second by moving app&service registration to the Boot app
- Files app now uses proper SD card mount point name (and multiple SD cards)
- Removed `TT_SCREENSHOT_MODE`

TactilityHeadless/Source/hal/SdCard.cpp

@@ -0,0 +1,17 @@
+#include "Tactility/hal/SdCard.h"
+#include "Tactility/hal/Device.h"
+
+namespace tt::hal {
+
+std::shared_ptr<SdCard> _Nullable findSdCard(const std::string& path) {
+    auto sdcards = findDevices<SdCard>(Device::Type::SdCard);
+    for (auto& sdcard : sdcards) {
+        if (sdcard->isMounted() && path.starts_with(sdcard->getMountPath())) {
+            return sdcard;
+        }
+    }
+
+    return nullptr;
+}
+
+}