Add copyright footer to gallery and photo pages

Renders a © 2000–<current-year> Ashik Salahudeen line under both the
index and each photo page. The year comes from time.Now().Year() at
render time so the range stays current without manual updates.

static/style.css

@@ -288,6 +288,20 @@ body {
   color: var(--fg2);
 }
 
+/* ── Site footer ───────────────────────────────────────────── */
+
+.site-footer {
+  max-width: 935px;
+  margin: 48px auto 0;
+  padding: 18px 20px 28px;
+  border-top: 1px solid var(--line);
+  text-align: center;
+  font-size: 12px;
+  color: var(--fg4);
+  font-family: monospace;
+  letter-spacing: 0.04em;
+}
+
 /* ── Responsive ────────────────────────────────────────────── */
 
 @media (max-width: 600px) {