Add shared building-block components: header, footer, CTAs, topographic background

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/TopographicBg.astro

@@ -0,0 +1,26 @@
+---
+interface Props {
+  opacity?: number;
+  lines?: number;
+}
+const { opacity = 0.12, lines = 8 } = Astro.props;
+
+const paths: string[] = [];
+const stepY = 100 / (lines + 1);
+for (let i = 1; i <= lines; i++) {
+  const y = i * stepY;
+  const amp = 4 + (i % 3) * 2;
+  paths.push(`M0,${y} Q25,${y - amp} 50,${y + amp * 0.6} T100,${y}`);
+}
+---
+<svg
+  class="absolute inset-0 w-full h-full pointer-events-none"
+  viewBox="0 0 100 100"
+  preserveAspectRatio="none"
+  aria-hidden="true"
+  style={`opacity:${opacity}`}
+>
+  <g fill="none" stroke="#f0b429" stroke-width="0.15" vector-effect="non-scaling-stroke">
+    {paths.map((d) => <path d={d} />)}
+  </g>
+</svg>