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

tools/README.md

@@ -130,6 +130,7 @@ tools/
     browser.py             the optional browser component (Playwright, `requirements-browser.txt`): `raw login`'s visible window and the headless fetch of a page a handler declares `render` - imported lazily, so a venv without it runs everything else
     sites/                 the site handlers behind `raw fetch`: a registry (`__init__.py`), the JSON file format (`site.schema.json`, `data.py`) and the stack's handlers as one file per website under `handlers/`, each stating the standard form of its URLs, the page furniture to leave out of the derived text, hint lines, which links are subpages for `raw fetch --scope`, a website's login page and the sign of a signed-in page, and whether its pages need a browser - all of it data (rewrites, selectors, text); the instance's own sit in `sites/` at the root
     filters/               the import filters behind `raw derive`: a registry (`__init__.py`) and one module per format family (HTML, mail, Outlook MSG, Office, PDF, ZIP), each registering the extensions it reads - standard library, or a package imported lazily so a missing one fails only its own format
+    backup.py              `backup init`/`backup run`'s core and the step `publish` runs after a push: the bare repository under `<target>/git`, the machine-data mirror under `<target>/<machine>/` with its manifest, and which synced folders `doctor` knows
     repo_capture.py        `raw capture`/`raw status`'s core: resolve a ref rule, fetch it into a bare cache, select files by glob as blobs, the `_capture.json` manifest - git with the host's credentials, never a prompt; plus the one write back, a single-file commit pushed without force for `export guidelines`
     guideline_export.py    `export guidelines`' core: select pages by `search` predicates, render them into one deterministic GUIDELINES.md, and recognise an export again (`EXPORT_MARKER`) - with no CLI attached
     search/                pluggable search backends, plus service.py - the search core