Optional sections: checkpoint tracker, admin/roles, login page

- dashboard.html: each section sits in OPTIONAL:<name> BEGIN/END blocks in
  the style, markup and script, with sample answers so a page with no bot
  shows it working. Core change: setUser records the role on <body>, so CSS
  hides admin-only parts from operators.
- templates/sections.py keeps the chosen sections and deletes the rest,
  markers included; it stops on a broken marker.
- templates/sections.md: what each section needs from the host (events,
  actions, desktop slot snippets, the role re-check, the login hand-off).
- SKILL.md step 5 asks one multi-select question and runs sections.py.
- Page check: checkpoint states, admin visibility by role and assign/remove,
  login theme and hand-off to auth or the stub. Cases skip on a generated
  page without the section; the template must carry all three. The harness
  signs in when the page has a login screen.
- tests/test_sections.py: no sections leave no trace, and that page still
  passes the page check.
- Eval runner: a-empty-sections variant (all three) and per-section checks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/README.md

@@ -17,6 +17,11 @@ uv run --with pytest --with playwright pytest tests
     `window.__calls` as `[slot, ...args]`.
   - To add a case, write a `test_*.py` file in `page_check/` that uses the `page`
     and `push(event, data)` fixtures from `conftest.py`.
+  - Optional-section cases (`test_optional_sections.py`) skip on a generated page
+    built without that section. The template must carry all of them. A page with
+    the login section is signed in (`login_result ok`) before each case.
+- `test_sections.py`: the optional-section strip tool keeps only the chosen
+  sections, and a page with none of them still passes the page check.
 - `evals/`: **Seam 2.** Runs the skills on a fixture project with `claude -p`,
   then grades the reply and runs the page check on the page it built: