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/references/rewrite-checklist.md

@@ -0,0 +1,10 @@
+# Rewrite checklist
+
+- `name` is lowercase, hyphenated, and matches the folder.
+- `description` says what the skill does and when to use it.
+- The default workflow has clear inputs and a concrete result.
+- Important limits have a reason; rules are not generic boilerplate.
+- Bundled resources are linked from `SKILL.md` and loaded only when needed.
+- Commands use relative paths and document prerequisites.
+- Mutations require an explicit user approval at the moment they occur.
+- The package has one normal and one boundary-case evaluation prompt.