施工(HEL-226): 实现登录门户与本机免密切换账号

用设备 Cookie 和授权表记住本机已验证账号，登录页按确认样图做成门户，不再把密码写进浏览器。

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

frontend/m/css/shell.css

@@ -246,6 +246,29 @@ body {
   padding-top: 8px;
 }
 
+.m-auth-accounts {
+  display: grid;
+  gap: 8px;
+  margin-bottom: 16px;
+}
+
+.m-auth-account {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  min-height: 48px;
+  padding: 0 14px;
+  border: 1px solid var(--border);
+  border-radius: 10px;
+  background: var(--surface);
+  color: var(--text-primary);
+}
+
+.m-auth-account span {
+  color: var(--action);
+  font-size: var(--font-size-label);
+}
+
 .m-auth-brand {
   text-align: center;
   margin: 24px 0 20px;