Centralize shared layout style contracts

webui/src/styles/components.css

@@ -3063,3 +3063,111 @@
 @keyframes file-drop-progress-spin {
   to { transform: rotate(360deg); }
 }
+
+/* Shared settings, placeholder, and administration layout contracts. */
+.placeholder-stack {
+  display: grid;
+  gap: 8px;
+  margin-top: 12px;
+}
+.placeholder-stack span {
+  display: block;
+  border: 1px dashed var(--line-dark);
+  border-radius: 6px;
+  background: var(--panel-soft);
+  padding: 10px 12px;
+  color: var(--muted);
+  font-weight: 700;
+}
+.compact-detail-list {
+  gap: 8px;
+}
+.settings-dashboard-grid {
+  align-items: start;
+}
+.settings-list {
+  display: grid;
+  gap: 12px;
+}
+.settings-target-row {
+  max-width: 520px;
+}
+.admin-secret {
+  display: block;
+  padding: 14px;
+  margin: 12px 0;
+  overflow-wrap: anywhere;
+  border: var(--border-line);
+  border-radius: var(--radius-sm);
+  background: var(--surface-muted);
+  font-size: 14px;
+  user-select: all;
+}
+.admin-json-preview {
+  max-height: 420px;
+  overflow: auto;
+  padding: 12px;
+  border: var(--border-line);
+  border-radius: var(--radius-sm);
+  background: var(--surface-muted);
+  white-space: pre-wrap;
+  word-break: break-word;
+}
+.admin-audit-grid .data-grid-scroll-region {
+  max-height: min(68vh, 720px);
+}
+.admin-audit-grid .data-grid-header-cell {
+  top: 0;
+}
+.admin-details-grid {
+  display: grid;
+  grid-template-columns: repeat(2, minmax(0, 1fr));
+  gap: 10px 18px;
+}
+.admin-details-grid > div {
+  min-width: 0;
+  padding: 10px 0;
+  border-bottom: var(--border-line);
+}
+.admin-details-grid dt {
+  color: var(--muted);
+  font-size: 12px;
+  font-weight: 700;
+  text-transform: uppercase;
+}
+.admin-details-grid dd {
+  margin: 4px 0 0;
+  overflow-wrap: anywhere;
+}
+.admin-governance-mode {
+  display: grid;
+  gap: 8px;
+}
+.admin-tenant-assignment-row {
+  display: grid;
+  grid-template-columns: minmax(0, 1fr) 140px;
+  align-items: center;
+  gap: 10px;
+}
+.admin-settings-form {
+  display: grid;
+  gap: 18px;
+}
+.admin-settings-form .card {
+  margin: 0;
+}
+.admin-managed-notice {
+  margin: 0 0 16px;
+  padding: 12px 14px;
+  border: 1px solid var(--info-muted-border);
+  border-radius: var(--radius-sm);
+  background: var(--info-bg);
+  color: var(--info-text-deep);
+  line-height: 1.45;
+}
+@media (max-width: 850px) {
+  .admin-details-grid,
+  .admin-tenant-assignment-row {
+    grid-template-columns: 1fr;
+  }
+}