Groundwork the guard tests of stage 0 stand on; no behaviour changes.
- internal/web/view/legacy_pages.txt: the redesign ratchet. Every page of
today's panel is listed as still old, plus @kit and @routes for the two
pieces of work whose tests stay quiet until they land. The list only
shrinks (enforced by CI in the next commits).
- internal/web/view/fixtures_test.go: the registry of fixtures the guards
render redesigned pages with. Empty until the kit page exists.
- web.go: route registration moves out of Handler() into muxes(), so a
test can ask the real muxes which pattern answers a path.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
