feat(11.1-01): DB migration, API routes, schema type updates for agent initials storage

- Add agentInitialsData text column to users table (drizzle/0009_luxuriant_catseye.sql)
- Add 'agent-initials' to SignatureFieldType union in schema.ts
- Update isClientVisibleField() to exclude both agent-signature and agent-initials
- Create GET/PUT /api/agent/initials route with auth guard and 50KB size limit

teressa-copeland-homes/drizzle/0009_luxuriant_catseye.sql

@@ -0,0 +1 @@
+ALTER TABLE "users" ADD COLUMN "agent_initials_data" text;