docs: add .agents workspace and the Astro refactor plan

Adds the agent-facing workspace and a 20-task plan for migrating the site
to Astro. Nothing here implements the refactor; these are briefs, rules and
templates that the task agents read.

- .agents/ holds context, rules, checklists, skills, specialist agents,
  component/page/config templates and gate scripts. It is vendor-neutral so
  MiniMax, Gemini and Codex can all read it; CLAUDE.md just points at
  AGENTS.md.
- .husky/ plus .lintstagedrc.json wire the three gate tiers. gate.sh locks on
  the shared git-common-dir so parallel worktrees serialise, and guards the
  assertion count in scripts/verify.mjs against a coverage drop.
- plans/astro-refactor/ carries the phase graph, per-task briefs and the
  model-routing recommendation.

These files must be tracked before fanning out: a worktree only checks out
tracked files, so an untracked plan is invisible to every agent working in one.

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

.agents/skills/motion/SKILL.md

@@ -0,0 +1,68 @@
+---
+name: motion
+description: Add or review animation on the ai-for-dummies site — transitions, state changes, view transitions. Use when any element moves, fades, or transforms, or when auditing existing motion for performance and reduced-motion support.
+---
+
+# Motion
+
+This is an editorial-print design. Motion is punctuation. Read
+[`../../rules/animation.md`](../../rules/animation.md) — it is binding; this is
+the procedure.
+
+## Decide it should move
+
+Answer out loud: **what does this motion tell the user that the static state
+does not?** Valid answers: something changed, attention needs directing to what
+changed, a layout shift needs smoothing. "It feels more polished" is not an
+answer — on this design it reads as generic.
+
+If there is no answer, ship it static. That is a legitimate, common outcome.
+
+## Build it
+
+```css
+.panel {
+  transition: opacity 180ms cubic-bezier(.2,0,0,1),
+              transform 180ms cubic-bezier(.2,0,0,1);
+}
+.panel[data-state='entering'] { opacity: 0; transform: translateY(6px); }
+```
+
+- **`transform` and `opacity` only.** Animating `width`/`height`/`top`/`left`
+  forces layout every frame and shows up as a failed INP (budget: 200ms).
+- 150–250ms for UI feedback; up to 400ms for a page transition.
+- One thing moves at a time. No staggered card cascades.
+- `will-change` only immediately before animating, removed after.
+- No animation library. This site's thesis is having no runtime dependencies.
+
+## Reduced motion is not optional
+
+```css
+@media (prefers-reduced-motion: reduce) {
+  * { animation-duration: .01ms !important; animation-iteration-count: 1 !important;
+      transition-duration: .01ms !important; scroll-behavior: auto !important; }
+}
+```
+
+Then **test it**: DevTools → Rendering → Emulate `prefers-reduced-motion:
+reduce`. The end state must still be correct and the UI still usable. Reduced,
+not broken.
+
+## Page transitions
+
+Astro's `<ClientRouter />` is the only sanctioned motion dependency. Before
+enabling it, verify:
+
+- JS disabled → full navigation still works
+- browser back/forward still works
+- the review desk's query-param deep links survive
+- `prefers-reduced-motion` is honoured
+
+## Audit an existing animation
+
+```bash
+grep -rn "transition\|animation\|@keyframes\|transform" src/ --include="*.astro" --include="*.css"
+```
+
+For each hit ask: does it animate a layout property? does it respect reduced
+motion? is there a stated purpose? Three questions, three possible fixes.