FC07 — real external IRQ and semaphore handoff

This card drives Hazard3 external IRQ input 5 through testbench MMIO. The external vector enters the official FreeRTOS full-context trap path, switches to xISRStack, calls an application ISR and returns through the context selected by portYIELD_FROM_ISR().

The ISR clears the hardware source before xSemaphoreGiveFromISR(). Because a priority-3 waiter is blocked while a priority-2 stimulus is interrupted, xHigherPriorityTaskWoken becomes pdTRUE. Evidence E07 proves that the waiter runs before E08, where the interrupted stimulus continues after its MMIO store.

make check
python3 /home/user/dev/workspace/stem/tools/card-layouts/tools/build_freertos_c_card.py .
python3 /home/user/dev/workspace/stem/tools/card-layouts/tools/render_card.py .