fix(GRO-1003): address CI typecheck and lint failures on PR #379

Typecheck fixes:
- telnyx.ts:48 — coerce undefined to null for signature param
- inbound.ts/outbound.ts — add null guards on .returning() results
- schema.ts — add updatedAt to messages table
- package.json — add uuid and @types/uuid

Lint fixes:
- telnyx.ts — remove unused resolveBusinessIdByMessagingNumber import
- inbound.ts — remove unused messageDirectionEnum, messageStatusEnum imports
- inbound.ts — remove unused buildFindOrCreateConversationParams function
- inbound.test.ts — remove unused resolveBusinessIdByMessagingNumber import
- outbound.test.ts — remove unused mockEq/mockAnd variables
- outbound.test.ts — fix vi.mock path for sms.js (../../sms.js)

packages/db/src/schema.ts

@@ -477,6 +477,7 @@ export const messages = pgTable(
     createdAt: timestamp("created_at").notNull().defaultNow(),
     deliveredAt: timestamp("delivered_at"),
     readByClientAt: timestamp("read_by_client_at"),
+    updatedAt: timestamp("updated_at").notNull().defaultNow(),
   },
   (t) => [
     index("idx_messages_conversation_id_created_at").on(