refactor: retire the hand-written site

Deletes the pre-Astro pages, scripts, and stylesheets that the migration
replaced, and moves the ones it did not replace out of the way.

Deleted (32 files): app.js, responsive.css, landing.css, rules/app.js,
rules/styles.css, skills/app.js, the ten route index.html files, and the
root hands-on/ copy, which is byte-identical to public/hands-on/ -- the
one the build actually ships.

Moved to legacy/ (12 files): styles.css, full-guide/audit.css,
chapters.css, skills/styles.css, skills-review/styles.css,
skills-review/change-lens.css, and the skills-review/app.js module graph.
These are not dead. The Astro pages import them and the build fails
without them, which the plan had not accounted for. They go to legacy/
rather than src/ because check-tokens.mjs sweeps src, and these files are
full of raw hex and unnamed breakpoints: moving one into src/ should mean
migrating it to tokens in the same change, not adding a scan exclusion.
The prettier, stylelint, and eslint ignore lists that already named these
files at their old paths now name legacy/ instead.

verify.mjs no longer reads app.js. The 102 Portuguese strings were
extracted from its translations.pt object before deletion into
.agents/snapshots/full-guide-pt.json -- a legacy capture, not a snapshot
of the Astro build, so the assertion still compares against an
independent source. The brace-matching helper's assertion is replaced by
one that rejects an empty snapshot entry, without which trimming the
snapshot would make the presence check pass vacuously. Count stays at 84.

audit-ui.mjs reads the ten pages from dist/ and resolves Astro's
base-absolute hrefs against it.

Before deleting anything, rendered-text-diff was run across all ten
routes plus both Portuguese pages: every one at parity, 0 missing and 0
extra. That comparison is not repeatable once the legacy files are gone.
computed-style-diff on /full-guide/ stays at 32 differences, so the moves
are style-neutral.

Docs updated to match: README, AGENTS.md, GATES.md, the architecture
context, the operations guide's lab instructions, and the three skills
that told you to serve the vanilla site.

Publishing is not part of this commit.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/pages/full-guide.astro

@@ -14,8 +14,8 @@ import CopyPrompt from '../components/islands/CopyPrompt.astro';
 import GuideSelector from '../components/islands/GuideSelector.astro';
 import LanguageToggle from '../components/islands/LanguageToggle.astro';
 import ReadingProgress from '../components/islands/ReadingProgress.astro';
-import '../../styles.css';
-import '../../full-guide/audit.css';
+import '../../legacy/styles/guide.css';
+import '../../legacy/styles/audit.css';
 
 type Entry<T extends { id: string }> = { data: T };
 const toRecord = <T extends { id: string }>(entries: Entry<T>[]) =>
@@ -1464,7 +1464,7 @@ const base = import.meta.env.BASE_URL;
       margin-left: auto;
     }
   }
-  /* token-gap: preserve the legacy full-guide layout threshold; task 20 can retire it with the legacy stylesheet */
+  /* token-gap: preserve the legacy full-guide layout threshold; responsive.css is gone, so this rule is now the only definition of it */
   @media (max-width: 600px) {
     .topbar-tools .edition {
       display: none;
@@ -3083,7 +3083,7 @@ const base = import.meta.env.BASE_URL;
       grid-column: auto;
     }
   }
-  /* token-gap: preserve the legacy full-guide layout threshold; task 20 can retire it with the legacy stylesheet */
+  /* token-gap: preserve the legacy full-guide layout threshold; responsive.css is gone, so this rule is now the only definition of it */
   @media (max-width: 600px) {
     .tree-detail {
       grid-template-columns: 1fr;