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/mod.rs

@@ -48,6 +48,7 @@ impl<P: Platform> Kernel<P> {
             }
             Syscall::Kill { process } => self.handle_kill(pid, process),
             Syscall::Revoke { slot } => self.handle_revoke(pid, slot),
+            Syscall::DropCap { slot } => self.handle_drop_cap(pid, slot),
             Syscall::Delegate {
                 slot,
                 to_endpoint,