fix: sched round-robin, cap slot OOB panic, clippy, make ci

- RunList -> intrusive FIFO, no starvation, no silent drop
- cap table sized to CapSlot range (kani caught OOB panic)
- snake food color test uses const
- kani cfg lint, RUST_MIN_STACK for big kernel struct in tests

crates/kernel/src/tests/capability.rs

@@ -197,3 +197,18 @@ fn revoke_syscall_without_revoke_permission_fails() {
         SyscallOutcome::Complete(SyscallResult::Error(_))
     ));
 }
+
+#[test]
+fn every_representable_slot_is_rejected_not_panicking() {
+    let (mut k, _) = kernel_with_process();
+    for raw in 1..=CapSlot::MAX {
+        let outcome = k.handle_syscall(Syscall::Send {
+            endpoint: CapSlot::new(raw).unwrap(),
+            message: domain::message::Message::empty(),
+        });
+        assert!(
+            matches!(outcome, SyscallOutcome::Complete(SyscallResult::Error(_))),
+            "slot {raw} should be an error"
+        );
+    }
+}