feat: enhance scheduling and management of email notifications

- Added functionality to cancel scheduled email notifications, improving user control over their email management.
- Implemented a query to list all scheduled emails for the current user, providing better visibility into upcoming notifications.
- Enhanced the email schema to support scheduling features, including a timestamp for scheduled delivery.
- Improved error handling and user feedback for email scheduling actions, ensuring a smoother user experience.

packages/backend/convex/schema.ts

@@ -501,11 +501,13 @@ export default defineSchema({
     enviadoPor: v.id("usuarios"),
     criadoEm: v.number(),
     enviadoEm: v.optional(v.number()),
+    agendadaPara: v.optional(v.number()), // timestamp para agendamento
   })
     .index("by_status", ["status"])
     .index("by_destinatario", ["destinatarioId"])
     .index("by_enviado_por", ["enviadoPor"])
-    .index("by_criado_em", ["criadoEm"]),
+    .index("by_criado_em", ["criadoEm"])
+    .index("by_agendamento", ["agendadaPara"]),
 
   configuracaoAcesso: defineTable({
     chave: v.string(), // "sessao_duracao", "max_tentativas_login", etc.