fix(05-04): pre-select document client and add manual email entry

- PreparePanel now receives separate assignedClientId (nullable) and
  defaultClientId props so it can distinguish an explicitly locked
  client from just a default
- When document already has assignedClientId: show locked read-only
  display; user cannot change the primary recipient
- When document has no assignedClientId: default to document owner in
  dropdown but allow changing; option to clear and enter email manually
- Added textarea for additional/CC email addresses (comma or newline
  separated) that is always visible for either mode
- POST /api/documents/[id]/prepare now accepts and stores emailAddresses
  array alongside assignedClientId
- Added email_addresses jsonb column to documents table via migration
  0004_military_maximus.sql

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

teressa-copeland-homes/drizzle/0004_military_maximus.sql

@@ -0,0 +1 @@
+ALTER TABLE "documents" ADD COLUMN "email_addresses" jsonb;