fix: keep the legacy :root palettes until task 20 deletes those files

Task 02b removed the `:root` palette blocks from `styles.css`,
`chapters.css`, `rules/styles.css` and `skills-review/styles.css` on the
grounds that `src/styles/tokens.css` is now the single source of truth.
That is true for the Astro pages, which import the token layer through
`BaseLayout.astro`. It is not true for the legacy pages, which are still
the live site: `index.html`, `full-guide/`, `agents/`, `models/`,
`summary/`, `rules/`, `skills/` and `skills-review/` link these
stylesheets standalone and never load `tokens.css`. Every `var(--paper)`,
`var(--ink)`, `var(--gold)` on those pages resolved to nothing.

Restores each file's own palette verbatim from main -- including the
drift (`--ink` is `#172f42` here and `#122534` there), because the
migration's contract is that the site looks exactly as it does today.
Adds `--font-sans` and `--font-mono` to each block so 02b's substitution
of those two variables for the literal font stacks keeps resolving.

Also adds `--allow-empty-input` to the stylelint lint-staged task. Since
`.stylelintignore` landed, a commit touching only legacy CSS gives
stylelint an all-ignored file list, which it treats as an error and which
made lint-staged revert this change wholesale.

The four blocks disappear with the files themselves at task 20.

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

.lintstagedrc.json

@@ -1,6 +1,6 @@
 {
   "*.{js,mjs,ts,astro}": ["prettier --write", "eslint --fix --max-warnings=0 --no-warn-ignored"],
-  "*.css": ["prettier --write", "stylelint --fix --max-warnings=0"],
+  "*.css": ["prettier --write", "stylelint --fix --max-warnings=0 --allow-empty-input"],
   "src/**/*.{astro,css}": ["node .agents/scripts/check-tokens.mjs"],
   "*.{json,md,yml,yaml}": ["prettier --write"]
 }

chapters.css

@@ -1 +1 @@
-*{box-sizing:border-box}body{margin:0;color:var(--ink);background:var(--paper);font:16px/1.6 var(--font-sans)}main{max-width:1400px;margin:auto;padding:0 5vw}.top{display:flex;justify-content:space-between;gap:20px;padding:24px 0;border-bottom:1px solid var(--line);font:700 11px var(--font-mono);letter-spacing:.08em;text-transform:uppercase}.top a{color:var(--ink);text-decoration:none}.hero{padding:100px 0 70px;max-width:950px}.eyebrow{color:var(--red);font:700 11px var(--font-mono);letter-spacing:.12em;text-transform:uppercase}.hero h1{margin:16px 0;font-size:clamp(52px,9vw,126px);line-height:.9;letter-spacing:-.07em}.hero h1 em,h2 em{font:400 .9em Georgia,serif;color:var(--red)}.hero p{max-width:680px;color:var(--muted);font-size:20px}.grid{display:grid;grid-template-columns:repeat(3,1fr);gap:1px;background:var(--line);border:1px solid var(--line);margin-bottom:100px}.card{min-height:220px;padding:28px;background:var(--paper)}.card b{color:var(--red);font:24px var(--font-mono)}.card h2{margin:18px 0 8px;font-size:25px;letter-spacing:-.04em}.card p{margin:0 0 14px;color:var(--muted)}.card a{color:var(--blue);font-weight:700}.model,.pipeline,.practice{display:grid;grid-template-columns:1fr 2fr;gap:50px;padding:80px 0;border-top:1px solid var(--line)}.model h2,.pipeline h2,.practice h2{margin:0;font-size:clamp(34px,5vw,70px);line-height:.95;letter-spacing:-.06em}.panel{padding:28px;background:var(--ink);color:var(--paper)}.panel strong{display:block;color:var(--gold);font:700 12px var(--font-mono);letter-spacing:.1em}.panel code{display:block;margin-top:18px;color:#d6e1e4;font:14px/1.8 var(--font-mono);white-space:pre-wrap}.steps{display:grid;gap:1px;background:var(--line)}.steps article{display:grid;grid-template-columns:70px 1fr;gap:20px;padding:20px;background:var(--paper)}.steps b{color:var(--red);font:20px var(--font-mono)}.steps strong{display:block}.steps span{color:var(--muted)}.links{display:flex;flex-wrap:wrap;gap:10px;margin:28px 0 70px}.links a{padding:10px 13px;color:var(--ink);border:1px solid var(--ink);text-decoration:none;font:11px var(--font-mono);text-transform:uppercase}.links a:hover{color:var(--paper);background:var(--ink)}footer{padding:30px 0 70px;color:var(--muted);font-size:13px}@media(max-width:800px){.grid,.model,.pipeline,.practice{grid-template-columns:1fr}.hero{padding:65px 0 45px}.model,.pipeline,.practice{gap:25px;padding:55px 0}}@media(max-width:520px){main{padding:0 16px}.top span{display:none}.hero h1{font-size:56px}.hero p{font-size:17px}.card{min-height:0}.steps article{grid-template-columns:45px 1fr}}
+:root{--ink:#122534;--paper:#f6f3ed;--line:#d0d5d2;--muted:#65717a;--blue:#215675;--gold:#ebbf58;--red:#a7483f;--font-sans:manrope,arial,sans-serif;--font-mono:'DM Mono',monospace;}*{box-sizing:border-box}body{margin:0;color:var(--ink);background:var(--paper);font:16px/1.6 var(--font-sans)}main{max-width:1400px;margin:auto;padding:0 5vw}.top{display:flex;justify-content:space-between;gap:20px;padding:24px 0;border-bottom:1px solid var(--line);font:700 11px var(--font-mono);letter-spacing:.08em;text-transform:uppercase}.top a{color:var(--ink);text-decoration:none}.hero{padding:100px 0 70px;max-width:950px}.eyebrow{color:var(--red);font:700 11px var(--font-mono);letter-spacing:.12em;text-transform:uppercase}.hero h1{margin:16px 0;font-size:clamp(52px,9vw,126px);line-height:.9;letter-spacing:-.07em}.hero h1 em,h2 em{font:400 .9em Georgia,serif;color:var(--red)}.hero p{max-width:680px;color:var(--muted);font-size:20px}.grid{display:grid;grid-template-columns:repeat(3,1fr);gap:1px;background:var(--line);border:1px solid var(--line);margin-bottom:100px}.card{min-height:220px;padding:28px;background:var(--paper)}.card b{color:var(--red);font:24px var(--font-mono)}.card h2{margin:18px 0 8px;font-size:25px;letter-spacing:-.04em}.card p{margin:0 0 14px;color:var(--muted)}.card a{color:var(--blue);font-weight:700}.model,.pipeline,.practice{display:grid;grid-template-columns:1fr 2fr;gap:50px;padding:80px 0;border-top:1px solid var(--line)}.model h2,.pipeline h2,.practice h2{margin:0;font-size:clamp(34px,5vw,70px);line-height:.95;letter-spacing:-.06em}.panel{padding:28px;background:var(--ink);color:var(--paper)}.panel strong{display:block;color:var(--gold);font:700 12px var(--font-mono);letter-spacing:.1em}.panel code{display:block;margin-top:18px;color:#d6e1e4;font:14px/1.8 var(--font-mono);white-space:pre-wrap}.steps{display:grid;gap:1px;background:var(--line)}.steps article{display:grid;grid-template-columns:70px 1fr;gap:20px;padding:20px;background:var(--paper)}.steps b{color:var(--red);font:20px var(--font-mono)}.steps strong{display:block}.steps span{color:var(--muted)}.links{display:flex;flex-wrap:wrap;gap:10px;margin:28px 0 70px}.links a{padding:10px 13px;color:var(--ink);border:1px solid var(--ink);text-decoration:none;font:11px var(--font-mono);text-transform:uppercase}.links a:hover{color:var(--paper);background:var(--ink)}footer{padding:30px 0 70px;color:var(--muted);font-size:13px}@media(max-width:800px){.grid,.model,.pipeline,.practice{grid-template-columns:1fr}.hero{padding:65px 0 45px}.model,.pipeline,.practice{gap:25px;padding:55px 0}}@media(max-width:520px){main{padding:0 16px}.top span{display:none}.hero h1{font-size:56px}.hero p{font-size:17px}.card{min-height:0}.steps article{grid-template-columns:45px 1fr}}