migrate stage build to native elc; chat restores from localStorage on return

Build pipeline
- build-stage.sh replaces the old in-Dockerfile bootstrap.py path. Host
  pre-compiles src/*.el into dist/main.c via the canonical native elc at
  foundation/el/dist/platform/elc and applies the stub-decl sed before
  docker buildx runs.
- Dockerfile.stage drops bootstrap.py + python3 from the builder stage
  and just runs cc on the host-supplied dist/main.c.
- Pre-rendered HTML shells under /srv/landing/ are now chowned to the
  landing user so the El page-builder's fs_write at startup can rewrite
  them — without that, post-COPY edits never reach the served HTML and
  the served page stays as the stale build-time fallback.

Chat restore
- session.verified + session.verifiedAt persist through localStorage so
  a return visit within 24h skips the Turnstile gate and lands directly
  in the restored conversation.
- restoreOrGreet() is the single source of truth for what shows up in
  the message pane after the gate clears: replays prior messages with
  skipSave, else drops the canned hello once and remembers it.
- applyVerifiedDom() hides the gate / reveals the chat row, called both
  from the verified-on-load path (DOMContentLoaded if loading, else
  immediate) and from the Turnstile callback.
- neuronDemoReset clears verified + verifiedAt so the gate returns next
  open.

Extracted JS assets (src/assets/js/*.js + manifest.json) and the
extract-js.py helper land here too — they match what the new build-stage
flow produces and removes the inline <script> blobs from the served HTML.

src/nav.el

@@ -52,63 +52,6 @@ fn nav() -> String {
   </div>
 </nav>
 
-<script>
-(function() {
-  var btn  = document.getElementById('nav-hamburger');
-  var menu = document.getElementById('nav-mobile');
-  var nav  = document.getElementById('nav');
-  if (!btn || !menu) return;
-
-  function close() {
-    menu.classList.remove('open');
-    btn.setAttribute('aria-expanded', 'false');
-  }
-  function open() {
-    menu.classList.add('open');
-    btn.setAttribute('aria-expanded', 'true');
-  }
-  function toggle() {
-    if (menu.classList.contains('open')) { close(); } else { open(); }
-  }
-
-  btn.addEventListener('click', function(e) { e.stopPropagation(); toggle(); });
-
-  // Dropdown — Mission
-  var ddBtn = document.querySelector('.nav-dropdown-btn');
-  var dd = document.querySelector('.nav-dropdown');
-  if (ddBtn && dd) {
-    ddBtn.addEventListener('click', function(e) {
-      e.stopPropagation();
-      var isOpen = dd.classList.contains('open');
-      dd.classList.toggle('open');
-      ddBtn.setAttribute('aria-expanded', isOpen ? 'false' : 'true');
-    });
-    dd.querySelectorAll('.nav-dropdown-item').forEach(function(a) {
-      a.addEventListener('click', function() { dd.classList.remove('open'); });
-    });
-    document.addEventListener('click', function() { dd.classList.remove('open'); });
-  }
-
-  // Close on any link inside mobile menu
-  menu.querySelectorAll('a').forEach(function(a) {
-    a.addEventListener('click', close);
-  });
-
-  // Close when clicking outside
-  document.addEventListener('click', function(e) {
-    if (!nav.contains(e.target)) { close(); }
-  });
-
-  // Close on Escape
-  document.addEventListener('keydown', function(e) {
-    if (e.key === 'Escape') { close(); }
-  });
-
-  // Close if viewport grows past breakpoint
-  window.addEventListener('resize', function() {
-    if (window.innerWidth > 1060) { close(); }
-  });
-})();
-</script>
+<script src=\"/assets/js/529d45d105c9.js\" defer></script>
 "
 }