feat: visual polish & UX — fade-in, theme toggle, scroll-to-top, footer, cursor, badge

- Add FadeIn component (IntersectionObserver scroll-reveal + load animation)
- Add dark/light theme toggle (useSyncExternalStore + localStorage)
- Add scroll-to-top button (appears after 300px scroll)
- Add configurable footer with social links (gallery.yaml)
- Add crosshair cursor on photo grid items
- Add 'X photos' count badge on subpage cover images
- Add light theme color palette in tokens.css

components/PasswordGate.module.css

@@ -0,0 +1,98 @@
+/* ── Password Gate Module ─────────────────────────── */
+
+.gate {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  min-height: calc(100vh - var(--header-height));
+  padding: 24px;
+}
+
+.card {
+  text-align: center;
+  padding: 48px 40px;
+  max-width: 400px;
+  width: 100%;
+  background: var(--bg-secondary);
+  border: 1px solid var(--border-subtle);
+  border-radius: var(--radius-lg);
+}
+
+.title {
+  font-family: var(--font-serif);
+  font-size: 1.8rem;
+  font-weight: 400;
+  letter-spacing: 0.02em;
+  margin-bottom: 8px;
+}
+
+.subtitle {
+  font-size: 0.85rem;
+  color: var(--text-secondary);
+  font-weight: 300;
+  margin-bottom: 32px;
+}
+
+.form {
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+}
+
+.input {
+  width: 100%;
+  padding: 12px 16px;
+  background: var(--bg-primary);
+  border: 1px solid var(--border-subtle);
+  border-radius: var(--radius-md);
+  color: var(--text-primary);
+  font-family: var(--font-sans);
+  font-size: 0.9rem;
+  outline: none;
+  transition: border-color var(--transition-fast);
+}
+
+.input:focus {
+  border-color: var(--accent);
+}
+
+.input::placeholder {
+  color: var(--text-muted);
+}
+
+.button {
+  padding: 12px 24px;
+  background: var(--accent);
+  color: var(--bg-primary);
+  border: none;
+  border-radius: var(--radius-md);
+  font-family: var(--font-sans);
+  font-size: 0.85rem;
+  font-weight: 500;
+  letter-spacing: 0.05em;
+  cursor: pointer;
+  transition: opacity var(--transition-fast);
+}
+
+.button:hover {
+  opacity: 0.9;
+}
+
+.button:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}
+
+.error {
+  margin-top: 12px;
+  font-size: 0.8rem;
+  color: #e74c3c;
+  font-weight: 400;
+}
+
+/* ── Responsive ──────────────────────────────────── */
+@media (max-width: 640px) {
+  .card {
+    padding: 36px 24px;
+  }
+}