fix: port full-guide responsive rules

Move the Astro-facing responsive layer out of responsive.css, retaining the exact legacy stylesheet for full-guide/index.html until task 20. Scope worktree and fleet overrides to their components so they can win against component base styles.

Do not delete responsive.css: the legacy page still loads it. Generated screenshot artifacts are deliberately untracked.

plans/astro-refactor/task-15e-responsive-css.md

@@ -36,10 +36,16 @@ together.
 
 ## Done when
 
-- [ ] Screenshot diffs empty at all four widths without `responsive.css`
+Superseded by the legacy-page amendment below. `responsive.css` cannot be
+deleted before task 20 because `full-guide/index.html` is still the live legacy
+route and deliberately links it.
+
+- [ ] Screenshot diffs reviewed at all required widths without an Astro import
+      of `responsive.css`
 - [ ] Ported rules live with the component that needs them, or in `tokens.css`
-- [ ] `responsive.css` deleted, and nothing references it
-- [ ] `pnpm run gate` green; 42 assertions intact
+- [ ] No Astro file or layout references `responsive.css`; the legacy page link
+      remains unchanged until task 20
+- [ ] `pnpm run gate` green; assertions intact
 
 ## Amendment — the screenshot step now actually works
 
@@ -109,6 +115,21 @@ everything up to the deletion:**
 - A list, in this file, of the rules that remain in `responsive.css` solely for
   the legacy page — that list is the deletion checklist task 20 will execute.
 
+### Task 20 deletion checklist
+
+`responsive.css` has no Astro consumer after this task. Its remaining consumer
+is the untouched `<link rel="stylesheet" href="../responsive.css">` in
+`full-guide/index.html`. Task 20 must retire that page before deleting the
+stylesheet. Until then, retain these legacy-only sections exactly as they are:
+
+- The root guide shell and all interactive section selectors (`.topbar` through
+  `.copy-status`), including their dark-surface colour values.
+- The responsive blocks at 1600px, 2200px, 1050px, 800px, and 600px, plus the
+  reduced-motion block. They continue to style the legacy HTML only.
+- The legacy page's `.route-meter span { height: var(--score) }` transition.
+  Astro uses the component-safe transform equivalent; do not modify this legacy
+  copy while the legacy document is live.
+
 Amend the "Done when" boxes to match before you start, and say in your final
 report that the file is intentionally still present.