fix: blocking_lock panic in status(), fingerprint copy-to-clipboard

- Change status() from blocking_lock to async lock().await —
  fixes "Cannot block the current thread from within a runtime" panic
  that froze the call timer and broke audio
- Click fingerprint to copy to clipboard (both connect and settings screens)
- Show "Copied!" feedback on click

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

desktop/src-tauri/src/engine.rs

@@ -333,8 +333,8 @@ impl CallEngine {
         !was
     }
 
-    pub fn status(&self) -> EngineStatus {
-        let parts = self.participants.blocking_lock();
+    pub async fn status(&self) -> EngineStatus {
+        let parts = self.participants.lock().await;
         EngineStatus {
             mic_muted: self.mic_muted.load(Ordering::Relaxed),
             spk_muted: self.spk_muted.load(Ordering::Relaxed),