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/domain/src/thread/mod.rs

@@ -303,3 +303,9 @@ impl ThreadTable {
             .filter(move |t| t.process() == process)
     }
 }
+
+impl Default for ThreadTable {
+    fn default() -> Self {
+        Self::new()
+    }
+}