Existing frontend: detect, report, then keep or restyle (ticket 03)

- templates/detect_frontend.py: finds plain HTML, React/Vue/Angular/Svelte apps
  and PyQt web views; prints location, stack, main colours, font and every
  token block (CSS custom properties, <style> tags, Tailwind config).
- templates/frontend.md: shared report / keep / restyle procedure, written
  so rpa-dashboard-ai can point to it.
- SKILL.md steps 1, 2 and 6 point to it.
- tests: detection self-check; fixture c-web-existing-frontend; eval entries
  c-keep and c-restyle (new pages only, per-question grading, checks on what
  changed in the existing files), both passing.

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

tests/README.md

@@ -25,5 +25,7 @@ uv run --with pytest --with playwright pytest tests
   ```
 
   Results go to `evals/results/<fixture>.json`. To add a fixture, add an entry to
-  `FIXTURES` in `run_eval.py`.
+  `FIXTURES` in `run_eval.py`. An entry with a `"fixture"` key reuses another
+  fixture folder with different answers: `c-keep` and `c-restyle` both run on
+  `c-web-existing-frontend`, and also check what changed in the files it already had.
 - `fixtures/<letter>-<name>/`: small test projects for the evals.