chore: consolidate the skill packages under .agents/

The repository had two skill directories. `skills/` held the four written
for this project; `.agents/skills/` held the ones the agent context refers
to. Nothing said which an agent should read, and `.agents/ORCHESTRATOR.md`
only ever pointed at the second.

Move the first four into `.agents/skills/` so there is one location, and
add the vendored packages this chapter work used: `animation-vocabulary`
and `improve-animations` (emilkowalski/skills), `teach` (mattpocock/skills),
plus a local `translation` skill and `audit-translations.mjs` for the EN/PT
pairs.

`skills-lock.json` pins the vendored three by source and content hash, so a
later re-vendor is a diff rather than a guess. `.claude/skills/` is
symlinks into `.agents/skills/`, which is what makes them loadable here
without a second copy on disk.

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

.agents/skills/editorial-playbook/SKILL.md

@@ -0,0 +1,45 @@
+---
+name: editorial-playbook
+description:
+  Use when building or reshaping a content-led interactive explainer, technical
+  playbook, or presentation-like static page; define the information
+  architecture, visual system, responsive behavior, bilingual copy, and minimal
+  interactive islands before coding.
+---
+
+# Editorial playbook
+
+Treat the page as a guided argument, not a dashboard. Give it one audience, one
+job, and one memorable thesis.
+
+## Workflow
+
+1. Write the chapter map before markup. Every section gets a stable slug,
+   number, title, purpose, and a single interaction or proof point when useful.
+   Reach for [page anatomy](references/page-anatomy.md) when adding a new
+   section.
+2. Compose from a few editorial primitives: label, thesis, pipeline or diagram,
+   comparison/table, code panel, callout, source card, and next-chapter link.
+   Keep the content model separate from rendering so more sections stay cheap.
+3. Use a restrained visual system: paper background, ink text, muted copy, one
+   cool accent, one warm signal, hairlines, and typography with a strong
+   display/body contrast. Prefer intentional asymmetry and generous rhythm over
+   cards everywhere.
+4. Keep runtime light. Use plain HTML/CSS/JS for static, mostly content-led
+   pages. Choose Astro or MDX only when many chapters need shared templates,
+   content collections, or build-time localization. Preserve an existing
+   framework when it already owns routing and tokens.
+5. Make the page bilingual at the content boundary. Pair English and Portuguese
+   strings, toggle the document language, persist the choice, and translate
+   labels, controls, status text, and dynamic details—not paths, commands, or
+   code.
+6. Make interactions causal and inspectable. One active state should explain one
+   idea; expose it with keyboard focus, an accessible state, a live status
+   region, copy feedback, and a reduced-motion path.
+7. Design for mobile, Full HD, and 4K. Use fluid type and spacing, cap readable
+   measure, stack dense regions at narrow widths, keep diagrams scrollable only
+   when semantically necessary, and test 390px, 1920px, and 3840px viewports.
+8. Finish with evidence: content verification, JavaScript syntax checks,
+   interaction tests, responsive browser checks, and a diff check. The section
+   is done when its content, dynamic states, links, and three viewport classes
+   pass.