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/skill-rewriter/SKILL.md

@@ -0,0 +1,34 @@
+---
+name: skill-rewriter
+description:
+  Rewrite an existing Agent Skill into a concise, safer, and more discoverable
+  package while preserving its intended capability. Use after a skill review or
+  when the user asks to improve a SKILL.md; do not alter original submissions in
+  place without explicit approval.
+---
+
+# Skill rewriter
+
+Create a separate revised package so the author can compare it with the
+original. Retain domain-specific facts that are supported by the source; replace
+generic filler with decisions the agent would otherwise miss.
+
+## Rewrite flow
+
+1. Read the original package and any review brief. Keep its intended job and
+   remove only unsupported assumptions, unsafe commands, or instructions that
+   conflict with the requested boundary.
+2. Write valid frontmatter: a lowercase hyphenated name matching the folder and
+   a description that states capability plus trigger terms.
+3. Use a short, friendly structure: Purpose, When to use, Inputs, Workflow,
+   Rules, Output, and Verification. Omit headings that add no decision-making
+   value.
+4. Move conditional detail to `references/`; add a script only for deterministic
+   repeated work and name its prerequisites. Use paths relative to the skill
+   root.
+5. Add concrete safety gates for mutation, credentials, and external systems.
+   Never preserve a secret in the rewritten package.
+6. Validate the new package and give the author an end-to-end explanation of the
+   changes and one next evaluation step.
+
+Read [the rewrite checklist](references/rewrite-checklist.md) for final checks.