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>

src/system_dns.rs

@@ -903,6 +903,7 @@ pub fn uninstall_service() -> Result<(), String> {
 
 /// Restart the service (kill process, launchd/systemd auto-restarts with new binary).
 pub fn restart_service() -> Result<(), String> {
+    #[cfg(any(target_os = "macos", target_os = "linux"))]
     let exe_path =
         std::env::current_exe().map_err(|e| format!("failed to get current exe: {}", e))?;
 
@@ -969,6 +970,7 @@ pub fn service_status() -> Result<(), String> {
     }
 }
 
+#[cfg(any(target_os = "macos", target_os = "linux"))]
 fn replace_exe_path(service: &str) -> Result<String, String> {
     let exe_path =
         std::env::current_exe().map_err(|e| format!("failed to get current exe: {}", e))?;
@@ -1411,6 +1413,22 @@ Wireless LAN adapter Wi-Fi:
         );
     }
 
+    #[test]
+    #[cfg(any(target_os = "macos", target_os = "linux"))]
+    fn replace_exe_path_substitutes_template() {
+        let plist = include_str!("../com.numa.dns.plist");
+        let unit = include_str!("../numa.service");
+
+        assert!(plist.contains("{{exe_path}}"), "plist missing placeholder");
+        assert!(unit.contains("{{exe_path}}"), "unit file missing placeholder");
+
+        let result = replace_exe_path(plist).expect("replace_exe_path failed for plist");
+        assert!(!result.contains("{{exe_path}}"));
+
+        let result = replace_exe_path(unit).expect("replace_exe_path failed for unit");
+        assert!(!result.contains("{{exe_path}}"));
+    }
+
     #[test]
     fn parse_ipconfig_skips_disconnected() {
         let sample = "\