feat(kernel): object lifetimes via slot generations

- SlotGenerations per table, never wraps, retires exhausted slots
- caps to dead/reused process, endpoint, region rejected
- endpoints owned, die w/ owner, waiters woken w/ error
- DropCap syscall + libkos wrapper
- irq table bounds-checked, routes dropped w/ thread
- self-kill terminates caller, exit_thread full cleanup
- sched run_now: switch to named thread, not queue head
- lifetime tests, fuzz kills/recreates, kani gen proofs

crates/kernel/src/syscall/lifecycle.rs

@@ -159,6 +159,10 @@ impl<P: Platform> Kernel<P> {
         };
 
         self.destroy_process(target_pid);
+        if target_pid == caller_pid {
+            // The caller no longer exists; nothing to return to.
+            return SyscallOutcome::TerminateCaller;
+        }
         SyscallOutcome::Complete(SyscallResult::Ok)
     }
 }