Various improvements (#461)

* **New Features**
  * Time and delay utilities added (ticks, ms, µs); SD card now uses an expansion-header CS pin; HTTP downloads warn when run on the GUI task and yield to avoid blocking.

* **Bug Fixes / Reliability**
  * Many hard-crash paths converted to guarded checks to reduce abrupt termination and improve stability.

* **Tests**
  * Unit tests added to validate time and delay accuracy.

* **Chores**
  * License header and build/macro updates.

TactilityKernel/Include/Tactility/FreeRTOS/port.h

@@ -5,6 +5,6 @@
 #include "FreeRTOS.h"
 
 #ifndef ESP_PLATFORM
-#define xPortInIsrContext(x) (false)
+#define xPortInIsrContext() (pdFALSE)
 #define vPortAssertIfInISR()
 #endif