docs: correct theme-fix rationale — local SQLite, not remote MySQL

The settings store is backed by the LOCAL SQLite config DB (wired before the
slow remote-MySQL logbook connect), so the "not ready" window is the brief
startup gap before OnStartup builds the store, not a MySQL delay. Fix behaviour
is unchanged; only the comments and changelog wording are corrected.

app.go

@@ -1835,12 +1835,13 @@ func (a *App) groupDigitalSlots() bool {
 
 func (a *App) GetUIPref(key string) (string, error) {
 	if a.settings == nil {
-		// Distinct from a genuinely-empty pref: the settings store isn't wired yet
-		// (still connecting the logbook DB — can take seconds on remote MySQL). The
-		// UI uses the error to keep RETRYING rather than treat it as "unset" and
-		// fall back to a default (the "dark theme reverts to light after an update"
-		// bug — localStorage was cleared by the update, and the DB read gave up too
-		// early while the backend was still starting).
+		// Distinct from a genuinely-empty pref: the (LOCAL SQLite) settings store
+		// isn't wired yet. There's a brief window at launch where the frontend can
+		// call this before OnStartup has opened the DB and built the store. The UI
+		// uses the error to keep RETRYING rather than treat it as "unset" and fall
+		// back to a default — the "dark theme reverts to light after an update" bug
+		// (the update cleared localStorage, and the DB read gave up too early while
+		// the store was still coming up).
 		return "", fmt.Errorf("settings store not ready")
 	}
 	return a.settings.Get(a.ctx, "ui."+key)