fix: gate exe_path and replace_exe_path for Windows clippy, add macOS CI

- Gate exe_path in restart_service() and replace_exe_path() behind
  #[cfg(any(target_os = "macos", target_os = "linux"))] to fix
  unused variable and dead code warnings on Windows
- Add macOS CI job (clippy + tests)
- Add test for template substitution in plist and systemd unit files

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -27,6 +27,17 @@ jobs:
       - name: audit
         run: cargo install cargo-audit && cargo audit
 
+  check-macos:
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+      - name: clippy
+        run: cargo clippy -- -D warnings
+      - name: test
+        run: cargo test
+
   check-windows:
     runs-on: windows-latest
     steps: