add settings editor component for unified on-site editing

Phase 3b of unified editing mode. The Settings tab now shows
context-specific forms: custom pages get editable title, slug,
meta, visibility and nav options; system pages get read-only info
with links to admin; product/collection pages show provider info.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

assets/css/admin/components.css

@@ -4600,6 +4600,72 @@
 /* Last group in a customise section (no border, tighter margin than theme-group) */
 .theme-group-flush { margin-bottom: 1rem; }
 
+/* ── Settings editor (on-site editor Settings tab) ── */
+
+.settings-editor-form {
+  display: flex;
+  flex-direction: column;
+  gap: 0.25rem;
+}
+
+.settings-slug-preview {
+  display: flex;
+  align-items: center;
+  gap: 0.25rem;
+}
+
+.settings-slug-preview .admin-input {
+  flex: 1;
+}
+
+.settings-nav-options {
+  padding-left: 1rem;
+  border-left: 2px solid var(--admin-border);
+}
+
+.settings-nav-row {
+  display: flex;
+  gap: 0.75rem;
+}
+
+.settings-nav-field {
+  flex: 1;
+}
+
+.settings-nav-field-sm {
+  flex: 0 0 5rem;
+}
+
+.settings-actions {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+  padding-top: 0.5rem;
+}
+
+.settings-save-indicator {
+  display: flex;
+  align-items: center;
+  gap: 0.25rem;
+  font-size: 0.875rem;
+  color: var(--admin-success);
+}
+
+.settings-save-error {
+  color: var(--admin-error);
+}
+
+.settings-admin-link {
+  padding-top: 0.5rem;
+  border-top: 1px solid var(--admin-border);
+}
+
+.settings-info-view {
+  display: flex;
+  flex-direction: column;
+  gap: 0.25rem;
+}
+
 /* ── Content width containers ── */
 
 .admin-content-narrow { max-width: 32rem; }