Compute refresh token expiry fresh on each sign-in

The expiry date was computed once at store init time and went stale
in long-running SPA sessions.

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

src/stores/login.ts

@@ -30,7 +30,6 @@ export const useLoginStore = defineStore('loginStore', {
     userData: {},
     isLoggedIn: false,
     rememberedReturnToUrl: "",
-    expired: (() => { const d = new Date(); d.setMonth(d.getMonth() + 6); return d.getTime(); })(), // 設定 Refresh Token 的到期日為半年後
   }),
   actions: {
     /**
@@ -51,7 +50,9 @@ export const useLoginStore = defineStore('loginStore', {
         const refresh_token = response.data.refresh_token;
         // 將 token 儲存在 cookie
         setCookieWithoutExpiration("luciaToken", accessToken);
-        setCookie("luciaRefreshToken", refresh_token, Math.ceil((this.expired - Date.now()) / (24 * 60 * 60 * 1000)));
+        const expiryDate = new Date();
+        expiryDate.setMonth(expiryDate.getMonth() + 6);
+        setCookie("luciaRefreshToken", refresh_token, Math.ceil((expiryDate.getTime() - Date.now()) / (24 * 60 * 60 * 1000)));
 
         this.isLoggedIn = true;
         setCookie("isLuciaLoggedIn", "true");