feat: question-count tiers, footer in main, pregunta footer

- Pricing: 0,99€/10q · 9,99€/200q · 19,99€/unlimited (all 30 days)
- DB: max_questions + questions_used columns on credits table;
  consumeCreditQuestion() atomically validates, creates question,
  and decrements quota in a single transaction
- Server: updated CREDIT_TIERS, /api/credito/estado returns questionsLeft,
  /api/pregunta/enviar returns updated questionsLeft after each submission
- pregunta.tsx: badge shows live question count; submit disabled when exhausted;
  questionsLeft synced to localStorage after each submission; Cloud Host footer added
- footer: moved from Standings sidebar into <main> (scrolls with game content);
  also added to all pregunta page states

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

pregunta.css

@@ -226,6 +226,12 @@ body {
   white-space: nowrap;
 }
 
+.pregunta__credit-badge--empty {
+  color: var(--text-muted);
+  background: rgba(255, 255, 255, 0.03);
+  border-color: var(--border);
+}
+
 /* ── Success banner ────────────────────────────────────────────── */
 
 .pregunta__success {
@@ -296,14 +302,20 @@ body {
 }
 
 .tier-card__price {
-  font-size: 22px;
+  font-size: 20px;
   font-weight: 700;
   color: var(--accent);
 }
 
 .tier-card__label {
   font-size: 12px;
-  color: var(--text-dim);
+  font-weight: 500;
+  color: var(--text);
+}
+
+.tier-card__sub {
+  font-size: 11px;
+  color: var(--text-muted);
 }
 
 /* ── Spinner ───────────────────────────────────────────────────── */
@@ -321,3 +333,25 @@ body {
 @keyframes pregunta-spin {
   to { transform: rotate(360deg); }
 }
+
+/* ── Site footer ───────────────────────────────────────────────── */
+
+.pregunta__footer {
+  margin-top: 24px;
+  padding-top: 16px;
+  border-top: 1px solid var(--border);
+  font-size: 11px;
+  color: var(--text-muted);
+  line-height: 1.9;
+  text-align: center;
+}
+
+.pregunta__footer a {
+  color: var(--text-dim);
+  text-decoration: none;
+}
+
+.pregunta__footer a:hover {
+  color: var(--text);
+  text-decoration: underline;
+}