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>

db.ts

@@ -95,17 +95,30 @@ export function markQuestionUsed(id: number): void {
   db.prepare("UPDATE questions SET status = 'used' WHERE id = $id").run({ $id: id });
 }
 
-/** Top 7 players by number of questions used, excluding anonymous. */
+/** Top 7 players by number of answers submitted, excluding anonymous. */
 export function getPlayerScores(): Record<string, number> {
   const rows = db
     .query(
-      "SELECT username, COUNT(*) as score FROM questions WHERE status = 'used' AND username != '' GROUP BY username ORDER BY score DESC LIMIT 7"
+      "SELECT username, COUNT(*) as score FROM user_answers WHERE username != '' GROUP BY username ORDER BY score DESC LIMIT 7"
     )
     .all() as { username: string; score: number }[];
   return Object.fromEntries(rows.map(r => [r.username, r.score]));
 }
 
-// ── Credits (question-count-based access) ───────────────────────────────────
+// ── User answers (submitted during live rounds) ──────────────────────────────
+
+db.exec(`
+  CREATE TABLE IF NOT EXISTS user_answers (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    round_num INTEGER NOT NULL,
+    text TEXT NOT NULL,
+    username TEXT NOT NULL,
+    token TEXT NOT NULL,
+    created_at DATETIME DEFAULT CURRENT_TIMESTAMP
+  );
+`);
+
+// ── Credits (answer-count-based access) ──────────────────────────────────────
 
 db.exec(`
   CREATE TABLE IF NOT EXISTS credits (
@@ -177,38 +190,35 @@ export function getCreditByOrder(orderId: string): {
 }
 
 /**
- * Atomically validates a credit token, creates a paid question, and increments
- * the usage counter. Returns null if the token is invalid, expired, or exhausted.
+ * Atomically validates a credit token, records a user answer for the given
+ * round, and decrements the answer budget. Returns null if the token is
+ * invalid or exhausted.
  */
-export function consumeCreditQuestion(
+export function submitUserAnswer(
   token: string,
+  roundNum: number,
   text: string,
-): { username: string; questionsLeft: number | null } | null {
+): { username: string; answersLeft: number } | null {
   const row = db
     .query(
-      "SELECT username, expires_at, max_questions, questions_used FROM credits WHERE token = $token AND status = 'active'"
+      "SELECT username, max_questions, questions_used FROM credits WHERE token = $token AND status = 'active'"
     )
     .get({ $token: token }) as {
     username: string;
-    expires_at: number;
-    max_questions: number | null;
+    max_questions: number;
     questions_used: number;
   } | null;
   if (!row) return null;
-  if (row.expires_at < Date.now()) return null;
-  if (row.max_questions !== null && row.questions_used >= row.max_questions) return null;
+  if (row.questions_used >= row.max_questions) return null;
 
-  const orderId = crypto.randomUUID();
   db.transaction(() => {
     db.prepare(
-      "INSERT INTO questions (text, order_id, username, status) VALUES ($text, $orderId, $username, 'paid')"
-    ).run({ $text: text, $orderId: orderId, $username: row.username });
+      "INSERT INTO user_answers (round_num, text, username, token) VALUES ($roundNum, $text, $username, $token)"
+    ).run({ $roundNum: roundNum, $text: text, $username: row.username, $token: token });
     db.prepare(
       "UPDATE credits SET questions_used = questions_used + 1 WHERE token = $token"
     ).run({ $token: token });
   })();
 
-  const questionsLeft =
-    row.max_questions === null ? null : row.max_questions - row.questions_used - 1;
-  return { username: row.username, questionsLeft };
+  return { username: row.username, answersLeft: row.max_questions - row.questions_used - 1 };
 }