Contacts cleanup

Read ../gog/SKILL.md and ../gog-contacts/SKILL.md first.

1. Detect duplicates without mutation:

   gog --account user@example.com --readonly contacts dedupe --match email,phone,name --json --wrap-untrusted
   

2. Present each proposed group with resource IDs and the fields that matched. Flag conflicts in names, organizations, notes, and non-empty phone/email values.

3. Preview the exact merge plan:

   gog --account user@example.com contacts dedupe --resource people/ONE \
     --resource people/TWO --apply --dry-run --json