feat: node info, build info and acrylic web theme

Squash of recent dev work: return_session login, backend switcher, line
detail timeline, overview strips, node platform/country/ISP info with flags
and icons, build info (version, tag, time) behind site.show_build, and the
acrylic display theme.

web/admin/src/admin.css

@@ -69,6 +69,27 @@
   background: var(--app-card);
 }
 
+/* 用户名太长时省略，不要和右边的按钮叠在一起 */
+.me {
+  flex-wrap: wrap;
+}
+
+.me .grow {
+  flex: 1 1 100px;
+  min-width: 0;
+}
+
+.me .grow > div {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.me .btn,
+.me .avatar {
+  flex: none;
+}
+
 .avatar {
   width: 32px;
   height: 32px;
@@ -192,3 +213,45 @@
     grid-template-columns: minmax(0, 1fr);
   }
 }
+
+/* 登录页：左边选后端，右边输入凭据 */
+.login .card.login-split {
+  width: min(760px, 100%);
+  padding: 0;
+  display: grid;
+  grid-template-columns: 260px minmax(0, 1fr);
+  overflow: hidden;
+}
+
+.login-side {
+  display: flex;
+  flex-direction: column;
+  gap: 24px;
+  padding: 32px 24px;
+  background: var(--app-card-inset);
+}
+
+.login-main {
+  padding: 32px;
+  align-content: start;
+}
+
+.login-main h2 {
+  font-size: 18px;
+  font-weight: 700;
+  word-break: break-all;
+}
+
+@media (max-width: 640px) {
+  .login .card.login-split {
+    grid-template-columns: minmax(0, 1fr);
+  }
+
+  .login-side {
+    padding: 24px;
+  }
+
+  .login-main {
+    padding: 24px;
+  }
+}