chore(gates): zero clippy warnings and a buildable sandbox example on Windows

The full-workspace gates had never run on this platform: collapsible
ifs in the Windows shell probe, a same-type cast in the crash handler,
an unused AsRawHandle import, and the sandbox smoke-test example
building its unix-only body (libc, kernel enforcement) unconditionally.
The example now stubs main off-unix; formatting reflow from cargo fmt.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KSy9S31pZNWXtRZNVJ1sDf

crates/codegen/kigi-tools/src/util/spawn.rs

@@ -15,7 +15,8 @@ pub use kigi_tty_utils::{
 pub async fn reap_killed_search_child(
     child: &mut tokio::process::Child,
 ) -> Option<std::process::ExitStatus> {
-    let status = kigi_tty_utils::reap_killed_bounded(child, kigi_tty_utils::KILL_REAP_TIMEOUT).await;
+    let status =
+        kigi_tty_utils::reap_killed_bounded(child, kigi_tty_utils::KILL_REAP_TIMEOUT).await;
     if status.is_none() {
         tracing::warn!(
             reap_timeout_secs = kigi_tty_utils::KILL_REAP_TIMEOUT.as_secs(),