feat(subpages): add optional sections with typographic TOC

- Add SubpageSectionConfig type to schema.ts
- Update config parser to handle sections with album overrides
- Refactor SubpageGridView to render TOC + section headers
- Add base CSS for subpage-toc and subpage-section in globals.css
- Add theme-specific overrides for all 5 themes (minimal, editorial,
  classic, noir, monograph)
- Update gallery.yaml.example and docs/gallery-config.md

app/themes/classic.css

@@ -191,3 +191,73 @@
   font-weight: 400;
   letter-spacing: 0.06em;
 }
+
+/* Subpage TOC: Cinzel uppercase with gold ornament separators */
+[data-preset='classic'] .subpage-toc {
+  margin-bottom: 56px;
+  justify-content: center;
+}
+
+[data-preset='classic'] .subpage-toc__entry+.subpage-toc__entry::before {
+  content: '◆';
+  padding: 0 14px;
+  font-size: 0.45rem;
+  color: var(--accent);
+}
+
+[data-preset='classic'] .subpage-toc__num {
+  display: none;
+}
+
+[data-preset='classic'] .subpage-toc__label {
+  font-family: var(--font-serif);
+  font-size: 0.75rem;
+  letter-spacing: 0.2em;
+  text-transform: uppercase;
+  font-weight: 400;
+}
+
+[data-preset='classic'] .subpage-toc__link {
+  color: var(--text-muted);
+}
+
+[data-preset='classic'] .subpage-toc__link:hover {
+  color: var(--accent);
+}
+
+/* Section: ornamental centered divider rule */
+[data-preset='classic'] .subpage-section__header {
+  text-align: center;
+  margin-bottom: 36px;
+}
+
+[data-preset='classic'] .subpage-section__title {
+  font-family: var(--font-serif);
+  font-size: 1.5rem;
+  letter-spacing: 0.15em;
+  text-transform: uppercase;
+  font-weight: 400;
+  margin-bottom: 4px;
+}
+
+[data-preset='classic'] .subpage-section__desc {
+  font-family: var(--font-caption);
+  font-style: italic;
+  font-size: 0.8rem;
+  color: var(--text-muted);
+}
+
+[data-preset='classic'] .subpage-section__rule {
+  background: none;
+  height: auto;
+  border: none;
+  text-align: center;
+  margin-top: 16px;
+}
+
+[data-preset='classic'] .subpage-section__rule::after {
+  content: '—◆—';
+  font-size: 0.55rem;
+  letter-spacing: 0.2em;
+  color: var(--accent);
+}