feat: embed propose-question widget inline in main game page

- Move /pregunta flow into a compact ProposeQuestion component
  rendered inside <main> above the footer
- Tier cards, username input, Redsys payment, polling, and question
  submission all work inline without leaving the game page
- Payment redirects now go to /?credito_ok=ORDER and /?ko=1
  so the game stays in view during the full payment cycle
- Badge shows live questions remaining; updates on each submission
- Removed /pregunta link from footer (functionality is now inline)
- .propose-* CSS: compact tier grid, textarea+button row, spinner

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

server.ts

@@ -635,8 +635,8 @@ const server = Bun.serve<WsData>({
         isTest,
         orderId,
         amount: tierInfo.amount,
-        urlOk: `${baseUrl}/pregunta?credito_ok=${orderId}`,
-        urlKo: `${baseUrl}/pregunta?ko=1`,
+        urlOk: `${baseUrl}/?credito_ok=${orderId}`,
+        urlKo: `${baseUrl}/?ko=1`,
         merchantUrl: `${baseUrl}/api/redsys/notificacion`,
         productDescription: `Acceso argument.es — ${tierInfo.label}`,
       });