Add El source files for all client-side JS

Recovers original JS from git history and ports it into proper El source
files under src/js/. Each file wraps the original JS in a native_js call
inside a main() function, making it valid El that compiles to a
self-contained IIFE via elc --target=js --bundle.

Files added:
  src/js/account-auth.el       - Supabase OTP magic-link (sendMagicLink)
  src/js/account-dashboard.el  - Account dashboard: session, plan card, family
  src/js/chat-widget.el        - Demo chat widget (neuronDemoToggle/Send/Reset)
  src/js/checkout-auth.el      - Checkout auth: OAuth, email sign-in/up
  src/js/checkout-free.el      - Free plan: auth-badge watch -> payment reveal
  src/js/checkout-stripe.el    - Stripe Payment Element (reads NEURON_CFG)
  src/js/enterprise.el         - Enterprise inquiry form + headcount filter
  src/js/environmental.el      - Efficiency calculator slider
  src/js/gallery.el            - Gallery nav, search/sort, Supabase voting
  src/js/main.el               - Share page voting + copyForPlatform
  src/js/marketplace.el        - Developer interest form
  src/js/nav.el                - Nav hamburger + Mission dropdown
  src/js/styles.el             - Landing: nav scroll, reveal, founding counter

src/environmental.el

@@ -44,7 +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 src=\"/assets/js/9bbad1ad5acb.js\" defer></script>
+        <script src=\"/js/environmental.js\" defer></script>
       </div>
 
       <div style=\"display:flex;flex-direction:column;gap:1.5rem;padding-top:1rem\">