fix: disable signal tests on Windows

Signal-based tests use Unix-specific libc::kill and POSIX signals
that don't exist on Windows. Disable these tests on Windows platform.

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

Co-Authored-By: Claude <[email protected]>

Author: ndbroadbent

renamify-cli/src/test_lock_signals.rs

@@ -1,4 +1,5 @@
 #[cfg(test)]
+#[cfg(unix)] // Signal tests only work on Unix-like systems
 #[allow(unused_mut)]
 mod signal_tests {
     use assert_cmd::Command as AssertCommand;