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/environmental.el

@@ -44,22 +44,7 @@ fn environmental() -> String {
           <p style=\"font-family:var(--body);font-size:0.75rem;color:var(--t3)\">Based on estimated token reduction applied to your monthly spend.</p>
         </div>
 
-        <script>
-        (function() {
-          var slider = document.getElementById('calc-slider');
-          var spendEl = document.getElementById('calc-spend');
-          var savingsEl = document.getElementById('calc-savings');
-          if (!slider) return;
-          function update() {
-            var monthly = parseInt(slider.value, 10);
-            var annual = Math.round(monthly * 0.35 * 12);
-            spendEl.textContent = '$' + monthly;
-            savingsEl.textContent = '$' + annual;
-          }
-          slider.addEventListener('input', update);
-          update();
-        })();
-        </script>
+        <script src=\"/assets/js/9bbad1ad5acb.js\" defer></script>
       </div>
 
       <div style=\"display:flex;flex-direction:column;gap:1.5rem;padding-top:1rem\">