doctor: the structure check's description names sites/CONTRACT.md, which doctor has required since the instance's site handlers (#210 close); 10.0.0-beta.5

Files changed:
- CHANGES.md
- VERSION
- docs/reference/commands/instance-health.md
- tools/CONTRACT.md
- tools/chemenu/commands/doctor.py

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

docs/reference/commands/instance-health.md

@@ -27,7 +27,7 @@ tools/wikitool doctor --json
 
 **Behaviour**
 
-- Checks dependencies (Python, ripgrep), author resolution, stack version, git identity/branch/remote, published skills, the kb/raw/reports/work/instructions structure, and generated files.
+- Checks dependencies (Python, ripgrep), author resolution, stack version, git identity/branch/remote, published skills, the kb/raw/reports/work/sites/instructions structure, and generated files.
 - Import filters (`import-filter-<name>`): one line for each `raw derive` format that reads through a package (PDF, Outlook `.msg`) - a `WARN` naming the package when it is missing, since that costs only its own format; fixed by running `tools/preflight.sh` again.
 - Tool paths (`tool-paths`): `.wikitool-tools.json` written by a preflight that finished, every tool `tools/prerequisites.txt` names for this platform recorded, and every recorded path still there - a `FAIL` otherwise, fixed by running `tools/preflight.sh` again (PowerShell 7: `tools/preflight.ps1`).
 - Install folder (`install-dir`): on Windows with long paths off, a `FAIL` when the folder holding `tools/` is longer than `tools/prerequisites.txt` allows (95 characters) - the limit the preflight enforces before it sets anything up.