backup: an instance backs up into a synced folder - backup init makes a bare repository under <target>/git its origin, backup run and publish mirror the machine data into <target>/<machine>/, doctor warns about .git in a synced folder (#186); 10.0.0-beta.10

Files changed:
- CHANGES.md
- INSTALL.md
- VERSION
- docs/explanation/configuration-tiers.md
- docs/how-to/README.md
- docs/how-to/back-up-to-a-synced-folder.md
- docs/reference/commands/README.md
- docs/reference/commands/git.md
- docs/reference/commands/instance-health.md
- docs/reference/configuration.md
- instructions/publish-cycle.md
- instructions/setup-instance.md
- tools/CONTRACT.md
- tools/README.md
- tools/chemenu/backup.py
- tools/chemenu/cli.py
- tools/chemenu/cli_contract.py
- tools/chemenu/commands/backup_cmd.py
- tools/chemenu/commands/doctor.py
- tools/chemenu/commands/git_publish.py
- tools/chemenu/config_shapes.py
- tools/chemenu/reference_doc.py
- tools/chemenu/tests/conftest.py
- tools/chemenu/tests/test_backup.py
- tools/chemenu/tests/test_config_shapes.py

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SnAJ7Z3CpVD3PRbN73QtU2

docs/how-to/README.md

@@ -30,5 +30,7 @@ Running the instance:
 - [Trace and score agent sessions](trace-and-score-sessions.md)
 - [Use 1Password for settings](use-1password-for-settings.md) - secrets and private values out
   of the tree, on the desktop and in CI
+- [Back up to a synced folder](back-up-to-a-synced-folder.md) - OneDrive and the like as the
+  backup of an instance without a git server, and restoring from it
 
 Installing a new instance is [INSTALL.md](../../INSTALL.md) at the repository root.