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/sync/api.rs

@@ -41,12 +41,14 @@ pub struct SyncTreeResponse {
 }
 
 #[derive(Debug, Serialize, Deserialize)]
+#[allow(dead_code)]
 pub struct SyncChangesResponse {
     pub changes: Vec<FileEntry>,
     pub server_time: String,
 }
 
 #[derive(Debug, Serialize, Deserialize)]
+#[allow(dead_code)]
 pub struct LockResponse {
     pub locked: Option<bool>,
     pub locked_by: Option<String>,
@@ -127,6 +129,7 @@ impl MiniCloudApi {
         Ok(data.tree)
     }
 
+    #[allow(dead_code)]
     pub async fn get_changes(&self, since: &str) -> Result<SyncChangesResponse, String> {
         let url = format!("{}/api/sync/changes?since={}", self.server_url, since);
         let resp = self.client.get(&url)