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-crash-handler/src/handler.rs

@@ -616,7 +616,7 @@ mod win {
             }
 
             let signal = exception_to_signal(exception_code);
-            let si_code = exception_code as i32;
+            let si_code = exception_code;
 
             // ExceptionInformation[1] holds the faulting address for ACCESS_VIOLATION.
             let si_addr = if exception_code == EXCEPTION_ACCESS_VIOLATION