sites: the instance writes its own site handlers as JSON files under sites/, the stack's learn.microsoft.com handlers become data files in the same format (#210); 10.0.0-beta.4

Files changed:
- .gitignore
- AGENTS.md
- CHANGES.md
- VERSION
- docs/explanation/architecture.md
- docs/how-to/README.md
- docs/how-to/write-a-site-handler.md
- docs/reference/commands/instance-health.md
- docs/reference/commands/raw-material-and-uploads.md
- docs/reference/configuration.md
- instructions/dev/doc-pull-through.md
- raw/CONTRACT.md
- sites/CONTRACT.md
- tools/CONTRACT.md
- tools/README.md
- tools/chemenu/commands/dist_cmd.py
- tools/chemenu/commands/docs_verify.py
- tools/chemenu/commands/doctor.py
- tools/chemenu/commands/git_publish.py
- tools/chemenu/commands/raw/fetch.py
- tools/chemenu/ownership.py
- tools/chemenu/sites/__init__.py
- tools/chemenu/sites/data.py
- tools/chemenu/sites/handlers/learn-microsoft-powershell-module.json
- tools/chemenu/sites/handlers/learn-microsoft.json
- tools/chemenu/sites/learn_microsoft.py
- tools/chemenu/sites/site.schema.json
- tools/chemenu/tests/test_dist_cmd.py
- tools/chemenu/tests/test_doctor.py
- tools/chemenu/tests/test_site_files.py
- tools/chemenu/toc.py

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

AGENTS.md

@@ -262,6 +262,7 @@ and this file.
 | `kb/` | [kb/CONTRACT.md](kb/CONTRACT.md) + `kb/CONVENTIONS.md` | What the stack enforces about a page (collections, linking, provenance), and beside it what this instance decided (language, naming, tone, labels, hedging) |
 | `reports/` | [reports/CONTRACT.md](reports/CONTRACT.md) | Why reports and traces are generated, gitignored, and carried into `kb/log.md` |
 | `work/` | [work/CONTRACT.md](work/CONTRACT.md) | Workshop runs: run keys, required files, why they are tracked, how a run closes |
+| `sites/` | [sites/CONTRACT.md](sites/CONTRACT.md) | The instance's own site handlers for `raw fetch`: file format, which handler applies, what a broken file does |
 | `tools/` | [tools/CONTRACT.md](tools/CONTRACT.md) | Command reference: one generated data record per command (name, synopsis, properties, exit status, retry policy), plus an index and the maintenance schedule - a command to look up (`wikitool <cmd> -h`, or a `grep` here) rather than a file to read through, as its own opening paragraph says |
 | `instructions/` | [instructions/CONTRACT.md](instructions/CONTRACT.md) | Instruction vs. skill, publishing, writing standard |