Remove iCloud Photos from borgmatic backup (#100)

## Summary
- Remove ~/Pictures from borgmatic source directories
- Update borgmatic and backup policy documentation
- Add Sifaka-Native Data section to clarify that photos (via Immich), music (via Navidrome), and video (via Jellyfin) are stored directly on Sifaka

## Deployment and Testing
- [ ] Run `mise run provision-indri -- --tags borgmatic --check --diff` to preview changes
- [ ] Run `mise run provision-indri -- --tags borgmatic` to apply
- [ ] Verify borgmatic config no longer includes ~/Pictures

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/100

ansible/roles/borgmatic/defaults/main.yml

@@ -16,7 +16,6 @@ borgmatic_source_directories:
   - /opt/homebrew/var/forgejo
   - /Users/erichblume/.config/borgmatic
   - /Users/erichblume/Documents
-  - /Users/erichblume/Pictures
 
 # Backup repository
 borgmatic_repositories: