Fix: filter empty strings in sync auth status check

disconnect_cloud_sync sets sync_gist_id to "" rather than deleting
it. Since get_setting returns Some("") for empty values, the
is_authenticated check (token.is_some() && gist_id.is_some())
incorrectly returns true after disconnect.

Add .filter(|s| !s.is_empty()) to all get_setting calls in
get_sync_auth_status, matching the pattern already used in
get_sync_status.

Relates to #195

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: prefrontalsys

src-tauri/src/commands/cloud_sync.rs

@@ -109,10 +109,10 @@ pub async fn connect_cloud_sync(
 #[tauri::command]
 pub fn get_sync_auth_status(db: State<'_, Arc<Mutex<Database>>>) -> Result<SyncAuthStatus, String> {
     let db = db.lock().map_err(|e| e.to_string())?;
-    let token = db.get_setting("github_token");
-    let username = db.get_setting("sync_username");
-    let gist_id = db.get_setting("sync_gist_id");
-    let gist_url = db.get_setting("sync_gist_url");
+    let token = db.get_setting("github_token").filter(|s| !s.is_empty());
+    let username = db.get_setting("sync_username").filter(|s| !s.is_empty());
+    let gist_id = db.get_setting("sync_gist_id").filter(|s| !s.is_empty());
+    let gist_url = db.get_setting("sync_gist_url").filter(|s| !s.is_empty());
     let has_gh = has_gh_cli();
 
     Ok(SyncAuthStatus {