The `stdio/env-security` e2e suite failed on Windows CI: its
bridge-crash case killed the bridge with bash's built-in `kill`, which
cannot terminate a Windows-native PID under Git Bash. The bridge stayed
alive, the unguarded `wait_for` timed out, and `set -e` aborted the
suite silently after test 8.

- Use the framework's `_kill_tree` and `wait_for_process_exit` helpers,
like the other bridge-kill suites
- Report a failed kill as a test failure instead of exiting silently

Refs the failing run:
https://github.com/apify/mcpc/actions/runs/38823604895/job/116725766327

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01FRPp1ESKxYjfpsVoQY95m8

Co-authored-by: Claude <noreply@anthropic.com>