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/nav.el

@@ -52,6 +52,6 @@ fn nav() -> String {
   </div>
 </nav>
 
-<script src=\"/assets/js/529d45d105c9.js\" defer></script>
+<script src=\"/js/nav.js\" defer></script>
 "
 }