feat: publish FreeRTOS C FC03 card

doc/assets/a4-application.puml

@@ -0,0 +1,21 @@
+@startuml
+!include card-uml-style.iuml
+scale 900 width
+left to right direction
+
+class "01  peerA\npriority 2 · CPU-bound" as PeerA <<task>>
+class "02  peerB\npriority 2 · CPU-bound" as PeerB <<task>>
+class "03  high_probe\npriority 0 → 3" as High <<task>>
+class "04  verifier\npriority 1 · runs last" as Verifier <<task>>
+
+PeerA <--> PeerB : tick time slicing\nA → B → A
+PeerA --> High : raise to priority 3
+High --> PeerA : preempts before call returns
+PeerA --> Verifier : stop requested after return
+PeerB --> Verifier : both peers self-delete
+
+note right of High
+  HIGH writes marker 2 and self-deletes.
+  peerA then writes marker 3.
+end note
+@enduml