chore: clean up migration comments and unused params

Remove obsolete Dart migration notes and route handling comments from splash-button.tsx and auth-machine.ts, and drop the unused `self` parameter from `chatWebSocketActor` callback signature.

src/stores/chat/chat-machine.actors.ts

@@ -184,7 +184,7 @@ export const loadMoreHistoryActor = fromPromise<
  * - cleanup 函数 → XState 在 parent state exit 时自动调用
  */
 export const chatWebSocketActor = fromCallback<ChatEvent, { token: string }>(
-  ({ sendBack, input, self }) => {
+  ({ sendBack, input }) => {
     console.log("[chat-machine] chatWebSocketActor ENTRY", {
       hasToken: !!input.token,
       tokenLength: input.token?.length ?? 0,