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/rules/animation.md

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+# Rule: animation
+
+This is an editorial-print design. Motion is punctuation, not decoration.
+
+## Budget
+
+- **Purpose or nothing.** Motion may signal a state change, direct attention to
+  what just changed, or smooth a layout shift. Nothing else.
+- Duration: **150–250ms** for UI feedback, up to 400ms for a page transition.
+  Longer reads as sluggish; shorter reads as a glitch.
+- Easing: `cubic-bezier(.2,0,0,1)` for entrances, `ease-out` for exits. Never
+  `linear` for anything a person watches. Never bounce/elastic — wrong register
+  for this design.
+- One thing moves at a time. Staggered cascades of cards are a template default;
+  this site has a point of view and does not do them.
+
+## `prefers-reduced-motion` is mandatory
+
+Several current stylesheets already honour it. Every new animation must:
+
+```css
+@media (prefers-reduced-motion: reduce) {
+  * { animation-duration: .01ms !important; animation-iteration-count: 1 !important;
+      transition-duration: .01ms !important; scroll-behavior: auto !important; }
+}
+```
+
+Reduced motion means *reduced*, not *broken*: the end state must still be
+correct and the interface still usable. Test it — in DevTools, Rendering →
+Emulate `prefers-reduced-motion`.
+
+## Performance
+
+- Animate **`transform` and `opacity` only.** They composite on the GPU.
+  Animating `width`, `height`, `top`, `left`, or `margin` forces layout on every
+  frame and will show up as a failed INP.
+- `will-change` only on an element about to animate, removed after. Leaving it
+  on permanently costs memory and can *hurt* performance.
+- Prefer CSS transitions. Reach for the Web Animations API only for sequencing
+  that CSS cannot express. Do not add an animation library — it is a runtime
+  dependency on a site whose thesis is having none.
+- INP budget is **200ms**. An animation that delays interaction response fails.
+
+## Astro view transitions
+
+If page transitions are wanted, use Astro's `<ClientRouter />`. It is the only
+sanctioned motion dependency, and it must:
+
+- degrade cleanly with JS disabled (it does — full navigation)
+- respect `prefers-reduced-motion`
+- not break the review desk's query-param deep links or browser back/forward
+
+## Accessibility
+
+- Never animate anything that conveys information on its own. Motion is
+  redundant reinforcement.
+- Nothing flashes more than three times per second.
+- Focus must stay visible throughout a transition, and focus order must not
+  change because of one.