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>

plans/astro-refactor/task-18-motion.md

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+# Task 18 — Motion pass
+
+**Agent**: `motion-designer` · **Model**: Gemini (perceptual judgement)
+**Depends on**: 15, 16 · **Parallel with**: 19
+**Worktree**: `.agents/scripts/worktree.sh start 18 motion`
+
+## Goal
+
+Audit the motion that exists, add only motion that earns its place, and make
+`prefers-reduced-motion` correct everywhere.
+
+## Order of work — audit first
+
+The audit is worth more than the additions.
+
+1. Inventory every `transition`, `animation`, `@keyframes`, `transform` in `src/`.
+2. Flag anything animating a layout property (`width`, `height`, `top`, `left`,
+   `margin`). Those force reflow every frame and fail the 200ms INP budget. The
+   Stylelint config already blocks new ones; find the ported ones.
+3. Confirm every animated element has a reduced-motion path, then **test it**
+   under DevTools emulation. Reduced means reduced, not broken — end states must
+   still be correct.
+
+## Then, sparingly
+
+Candidates, each needing a written purpose:
+
+- tab panel change in the guide (state change — justified)
+- review-desk detail swap on selection (state change — justified)
+- vote widget tally update (feedback — justified)
+
+`transform` and `opacity` only. 150–250ms. `cubic-bezier(.2,0,0,1)`. One thing
+moves at a time — no staggered card cascades; this design has a point of view
+and staggering reads as a template.
+
+## View transitions — optional, decide explicitly
+
+Astro's `<ClientRouter />` is the only sanctioned motion dependency. If adopted,
+verify: JS-disabled navigation, browser back/forward, the review desk's six
+query params, and reduced motion. If any fails, do not ship it.
+
+## Done when
+
+- [ ] Zero animations on layout properties
+- [ ] Every animation has a one-line written purpose
+- [ ] Reduced-motion tested under emulation; end states correct
+- [ ] Before/after captures attached; `npm run gate` green