feat: add error handling modal to ChatWindow and improve call initiation logic

- Introduced ErrorModal in ChatWindow to display error messages related to call initiation issues.
- Enhanced error handling during call initiation to provide user-friendly feedback based on different error scenarios.
- Refactored backend queries to streamline the retrieval of active calls, ensuring accurate status checks.
- Updated function names for clarity and consistency in the backend call management logic.

packages/backend/convex/schema.ts

@@ -860,7 +860,6 @@ export default defineSchema({
     criadoEm: v.number(),
   })
     .index("by_conversa", ["conversaId", "status"])
-    .index("by_conversa_ativa", ["conversaId", "status"])
     .index("by_criado_por", ["criadoPor"])
     .index("by_status", ["status"])
     .index("by_room_name", ["roomName"]),