fix: simplify nav with Start dropdown and move Get in touch to footer

Nav now shows: How it works, Features, Start (dropdown: Docs, Source,
Releases). Get in touch moved to footer. Cleaner on mobile.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

website/style.css

@@ -106,6 +106,45 @@ header nav a:hover { color: var(--text); opacity: 1; }
   font-weight: 500;
 }
 
+.nav-dropdown {
+  position: relative;
+}
+
+.nav-dropdown-toggle {
+  cursor: pointer;
+}
+
+.nav-dropdown-menu {
+  display: none;
+  position: absolute;
+  top: 100%;
+  right: 0;
+  margin-top: 0.5rem;
+  background: var(--surface);
+  border: 1px solid var(--border);
+  border-radius: 0.5rem;
+  padding: 0.5rem 0;
+  min-width: 140px;
+  z-index: 100;
+}
+
+.nav-dropdown-menu a {
+  display: block;
+  padding: 0.4rem 1rem;
+  font-size: 0.82rem;
+  color: var(--text-secondary);
+}
+
+.nav-dropdown-menu a:hover {
+  background: var(--surface-hover);
+  color: var(--text);
+  opacity: 1;
+}
+
+.nav-dropdown:hover .nav-dropdown-menu {
+  display: block;
+}
+
 /* Hero */
 .hero {
   padding: 10vh 0 6vh;