feat: users answer alongside AI instead of proposing questions

- Core mechanic change: users now submit answers to the live prompt,
  competing alongside AI models; answers broadcast to all viewers
- New pricing (no time limit, pure count-based, refillable):
  0,99€ = 10 resp · 9,99€ = 300 resp · 19,99€ = 1000 resp
- DB: new user_answers table; submitUserAnswer() atomically validates
  credit, inserts answer, decrements budget; JUGADORES leaderboard
  now scores by user_answers count
- server: /api/respuesta/enviar endpoint; credit activation sets
  expires_at 10 years out (effectively no expiry); answers injected
  into live round state and broadcast via WebSocket
- frontend: ProposeAnswer widget shows current prompt, textarea active
  during answering phase, tracks per-round submission state;
  Arena shows Respuestas del público section live

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

server.ts

@@ -7,8 +7,7 @@ import broadcastHtml from "./broadcast.html";
 import preguntaHtml from "./pregunta.html";
 import {
   clearAllRounds, getRounds, getAllRounds,
-  createPendingQuestion, markQuestionPaid,
-  createPendingCredit, activateCredit, getCreditByOrder, consumeCreditQuestion,
+  createPendingCredit, activateCredit, getCreditByOrder, submitUserAnswer,
   getPlayerScores,
 } from "./db.ts";
 import { buildPaymentForm, verifyNotification, decodeParams, isPaymentApproved } from "./redsys.ts";
@@ -116,10 +115,10 @@ const VIEWER_VOTE_BROADCAST_DEBOUNCE_MS = parsePositiveInt(
 const AUTOPAUSE_DELAY_MS = parsePositiveInt(process.env.AUTOPAUSE_DELAY_MS, 60_000);
 const ADMIN_COOKIE = "argumentes_admin";
 
-const CREDIT_TIERS: Record<string, { days: number; amount: number; label: string; maxQuestions: number | null }> = {
-  basico:    { days: 30, amount: 99,   label: "10 preguntas",        maxQuestions: 10   },
-  pro:       { days: 30, amount: 999,  label: "200 preguntas",       maxQuestions: 200  },
-  ilimitado: { days: 30, amount: 1999, label: "Preguntas ilimitadas", maxQuestions: null },
+const CREDIT_TIERS: Record<string, { amount: number; label: string; maxAnswers: number }> = {
+  basico: { amount: 99,   label: "10 respuestas",   maxAnswers: 10   },
+  pro:    { amount: 999,  label: "300 respuestas",  maxAnswers: 300  },
+  full:   { amount: 1999, label: "1000 respuestas", maxAnswers: 1000 },
 };
 const ADMIN_COOKIE_MAX_AGE_SECONDS = 60 * 60 * 24 * 30;
 
@@ -561,7 +560,8 @@ const server = Bun.serve<WsData>({
             if (credit && credit.status === "pending") {
               const tierInfo = CREDIT_TIERS[credit.tier];
               if (tierInfo) {
-                const expiresAt = Date.now() + tierInfo.days * 24 * 60 * 60 * 1000;
+                // No time limit — set expiry 10 years out so existing checks pass
+                const expiresAt = Date.now() + 10 * 365 * 24 * 60 * 60 * 1000;
                 const activated = activateCredit(orderId, expiresAt);
                 if (activated) {
                   log("INFO", "redsys", "Credit activated", {
@@ -613,14 +613,14 @@ const server = Bun.serve<WsData>({
 
       const tierInfo = CREDIT_TIERS[tier];
       if (!tierInfo) {
-        return new Response("Tier inválido (basico | pro | ilimitado)", { status: 400 });
+        return new Response("Tier inválido (basico | pro | full)", { status: 400 });
       }
       if (!username || username.length < 1 || username.length > 30) {
         return new Response("El nombre debe tener entre 1 y 30 caracteres", { status: 400 });
       }
 
       const orderId = String(Date.now()).slice(-12);
-      createPendingCredit(username, orderId, tier, tierInfo.maxQuestions);
+      createPendingCredit(username, orderId, tier, tierInfo.maxAnswers);
 
       const isTest = process.env.REDSYS_TEST !== "false";
       const terminal = process.env.REDSYS_TERMINAL ?? "1";
@@ -638,7 +638,7 @@ const server = Bun.serve<WsData>({
         urlOk: `${baseUrl}/?credito_ok=${orderId}`,
         urlKo: `${baseUrl}/?ko=1`,
         merchantUrl: `${baseUrl}/api/redsys/notificacion`,
-        productDescription: `Acceso argument.es — ${tierInfo.label}`,
+        productDescription: `argument.es — ${tierInfo.label}`,
       });
 
       log("INFO", "credito", "Credit purchase initiated", {
@@ -664,8 +664,9 @@ const server = Bun.serve<WsData>({
           headers: { "Content-Type": "application/json", "Cache-Control": "no-store" },
         });
       }
-      const questionsLeft =
-        credit.maxQuestions === null ? null : credit.maxQuestions - credit.questionsUsed;
+      const answersLeft = credit.maxQuestions === null
+        ? 0
+        : credit.maxQuestions - credit.questionsUsed;
       return new Response(
         JSON.stringify({
           found: true,
@@ -676,7 +677,7 @@ const server = Bun.serve<WsData>({
                 username: credit.username,
                 expiresAt: credit.expiresAt,
                 tier: credit.tier,
-                questionsLeft,
+                answersLeft,
               }
             : {}),
         }),
@@ -684,14 +685,14 @@ const server = Bun.serve<WsData>({
       );
     }
 
-    if (url.pathname === "/api/pregunta/enviar") {
+    if (url.pathname === "/api/respuesta/enviar") {
       if (req.method !== "POST") {
         return new Response("Method Not Allowed", {
           status: 405,
           headers: { Allow: "POST" },
         });
       }
-      if (isRateLimited(`pregunta:${ip}`, 20, WINDOW_MS)) {
+      if (isRateLimited(`respuesta:${ip}`, 20, WINDOW_MS)) {
         return new Response("Too Many Requests", { status: 429 });
       }
 
@@ -708,16 +709,26 @@ const server = Bun.serve<WsData>({
       if (!token) {
         return new Response("Token requerido", { status: 401 });
       }
-      if (text.length < 10 || text.length > 200) {
-        return new Response("La pregunta debe tener entre 10 y 200 caracteres", { status: 400 });
+      if (text.length < 3 || text.length > 150) {
+        return new Response("La respuesta debe tener entre 3 y 150 caracteres", { status: 400 });
       }
 
-      const result = consumeCreditQuestion(token, text);
-      if (!result) {
-        return new Response("Crédito no válido, expirado o sin preguntas disponibles", { status: 401 });
+      const round = gameState.active;
+      if (!round || !round.prompt) {
+        return new Response("No hay ronda activa", { status: 409 });
       }
-      log("INFO", "pregunta", "Question submitted via credit", { username: result.username, ip });
-      return new Response(JSON.stringify({ ok: true, questionsLeft: result.questionsLeft }), {
+
+      const result = submitUserAnswer(token, round.num, text);
+      if (!result) {
+        return new Response("Crédito no válido o sin respuestas disponibles", { status: 401 });
+      }
+
+      // Add to live round state and broadcast
+      round.userAnswers = [...(round.userAnswers ?? []), { username: result.username, text }];
+      broadcast();
+
+      log("INFO", "respuesta", "User answer submitted", { username: result.username, round: round.num, ip });
+      return new Response(JSON.stringify({ ok: true, answersLeft: result.answersLeft }), {
         status: 200,
         headers: { "Content-Type": "application/json", "Cache-Control": "no-store" },
       });