fix: remove medium theme, fix navbar re-render, fix Node.js env loading

- Remove 'medium' theme from dashboard and marketplace; keep only light/dark
- Marketplace: move public pages into (public)/ route group so header/footer
  persist across navigations without re-rendering (eliminates usePathname)
- MarketplaceShell is now a pure context provider; chrome lives in
  (public)/layout.tsx which Next.js holds stable across navigations
- WorkspaceFrame: remove history.replaceState and standalone-route logic
- Docker API: bypass npm run dev to avoid node --env-file in containers
- Add scripts/run-with-env-file.cjs for Node.js < 20.6 compatibility;
  update apps/api/package.json dev script to use it

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/dashboard/src/app/sign-in/[[...sign-in]]/SignInPageClient.tsx

@@ -92,7 +92,7 @@ export default function SignInPageClient({ embedded = false }: { embedded?: bool
     }
 
     if (
-      (requestedTheme === 'light' || requestedTheme === 'medium' || requestedTheme === 'dark') &&
+      (requestedTheme === 'light' || requestedTheme === 'dark') &&
       requestedTheme !== theme
     ) {
       setTheme(requestedTheme)