fix(HEL-243): 当前账号可点击返回，避免切换死路

当前账号行原先只显示对号、不可点击，单账号时只能关网页。现改为整行继续使用且不重新签发会话，并带回切换前的业务页。

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

frontend/shared/auth.css

@@ -2389,6 +2389,18 @@ body.login-portal {
   font-size: 16px;
 }
 
+.login-account-action {
+  display: grid;
+
+  justify-items: end;
+
+  gap: 2px;
+
+  color: var(--action);
+
+  font-size: var(--font-size-caption);
+}
+
 .login-account-remove {
   display: grid;
 

frontend/shared/session.js

@@ -196,7 +196,13 @@ async function changeAccountPassword(event) {
 
 async function switchAccount() {
   toggleAccountDropdown(false);
-  window.location.assign("/login/");
+  const params = new URLSearchParams();
+  const next = `${window.location.pathname}${window.location.search}${window.location.hash}`;
+  if (next.startsWith("/") && !next.startsWith("//") && next !== "/login" && !next.startsWith("/login/") && !next.startsWith("/login?")) {
+    params.set("next", next);
+  }
+  const query = params.toString();
+  window.location.assign("/login/" + (query ? `?${query}` : ""));
 }