fix: Alle Rust-Warnings bereinigt

- unused variables: Underscore-Prefix (_real_path, _had_changes, _file_id)
- dead_code: #[allow(dead_code)] fuer zukuenftige Methoden
  (open_cloud_file, close_cloud_file, get_changes, LockResponse, SyncChangesResponse)

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

clients/desktop/src-tauri/src/lib.rs

@@ -19,7 +19,7 @@ use std::collections::HashMap;
 /// Tracks a file opened from a .cloud placeholder
 #[derive(Clone, Debug)]
 struct OpenedFile {
-    file_id: i64,
+    _file_id: i64,
     real_path: PathBuf,
     cloud_name: String, // original .cloud filename
 }
@@ -255,7 +255,7 @@ async fn open_cloud_file(state: State<'_, AppState>, cloud_path: String) -> Resu
 
     // Track opened file for auto-close detection
     state.opened_files.lock().unwrap().insert(file_id, OpenedFile {
-        file_id,
+        _file_id: file_id,
         real_path: real_path.clone(),
         cloud_name: path.file_name().unwrap().to_string_lossy().to_string(),
     });
@@ -592,7 +592,7 @@ fn start_background_sync(
 
             let state = app_w.state::<AppState>();
             let watchers = state.watchers.lock().unwrap();
-            let mut had_changes = false;
+            let mut _had_changes = false;
 
             for watcher in watchers.iter() {
                 while let Ok(change) = watcher.receiver.try_recv() {
@@ -608,7 +608,7 @@ fn start_background_sync(
                         ChangeKind::Deleted => format!("Geloescht: {}", name),
                     };
                     let _ = app_w.emit("file-change", msg);
-                    had_changes = true;
+                    _had_changes = true;
                     last_change = std::time::Instant::now();
                     pending = true;
                 }