fix(uninstall): precise PAI-owned file targeting, no false claims

Previous version listed agents/, lib/, plugins/, CLAUDE.md, README.md,
and .gitignore as PAI-owned in the preview — all of which are also used
by Claude Code or users directly.

Now the script is fine-grained:
- "PAI-exclusive" section: only skills/, VoiceServer/, PAI-Install/,
  statusline-command.sh, LaunchAgent/log — things with no Claude Code
  equivalent
- "PAI files in shared dirs": removes the 13 known PAI agent files by
  name from agents/ (leaves any user-added agents); removes
  lib/migration/ specifically (cleans lib/ if then empty)
- install.sh: only removed if grep confirms it references PAI-Install/
- CLAUDE.md: only removed if it contains PAI marker text (unmodified)
- README.md, .gitignore: skipped entirely (too generic to claim)
- plugins/: moved to backup-and-confirm section (user may have
  installed plugins)

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

Author: gabehamilton