desktop: rustfmt the two new preference helpers

Verified locally this time rather than in CI. The ci-tauri image is already on
this machine, so `cargo fmt --check` can run in a throwaway container against
the exact toolchain CI uses — no test run, no build, no local stack, just the
formatter. Four consecutive pushes had failed on formatting alone; that class
of failure is now catchable before it costs a cycle.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SreJkbxB4gx8pPsu8QbLPi

desktop/src-tauri/src/update.rs

@@ -92,7 +92,10 @@ fn self_update_blocker() -> Option<String> {
 fn read_channel(db: &State<'_, Db>) -> Result<Channel, String> {
     let conn = db.0.lock().map_err(|e| e.to_string())?;
     let raw = store::pref(&conn, CHANNEL_PREF).map_err(|e| e.to_string())?;
-    Ok(raw.as_deref().map(Channel::parse).unwrap_or(Channel::Stable))
+    Ok(raw
+        .as_deref()
+        .map(Channel::parse)
+        .unwrap_or(Channel::Stable))
 }
 
 #[tauri::command]