Consolidate pkg/chats and pkg/chatbackup into single package

[CodeMonkeyCybersecurity]

Problem

Two packages provide AI chat backup functionality:

• pkg/chatbackup/ (15 files, ~156KB) - the actively used, more developed version
• pkg/chats/ (4 files, ~544 lines) - an earlier version from a parallel development stream

Proposed Solution

1. Audit both packages for unique functionality
2. Port any missing functionality to pkg/chatbackup/
3. Delete pkg/chats/

Root Cause

Parallel development streams independently created chat backup packages.