Block manual send reservation for unreleased shared numbers

Implement shared-number detection in reserveOutreachSend: reject manual WhatsApp sends with HTTP 409 when the destination number is shared across 2+ leads and hasn't been explicitly released via override.

- Add test: reserveOutreachSend bloqueia numero compartilhado sem override e libera com override
- Add check in reserveOutreachSend right after isOptedOut check
- Uses isNumberSharedAcrossLeads and isSharedNumberOverridden from Task 1

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/db.mjs

@@ -1127,6 +1127,11 @@ export function reserveOutreachSend(db, {
       error.statusCode = 409;
       throw error;
     }
+    if (isNumberSharedAcrossLeads(db, normalized) && !isSharedNumberOverridden(db, normalized)) {
+      const error = new Error('numero compartilhado por multiplos leads (revise em Configuracoes antes de enviar)');
+      error.statusCode = 409;
+      throw error;
+    }
     const limit = Number(getSetting(db, 'outreach.mensagensPorDia', '10')) || 0;
     const used = countDailyOutreachUsage(db, { origem: 'manual' });
     if (used >= limit) {