feat: publish FreeRTOS C FC07 card

README.md

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+# 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.
+
+```sh
+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 .
+```