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-08-route-cards.md

@@ -0,0 +1,37 @@
+# Task 08 — Route cards and grid group
+
+**Agent**: `component-builder` · **Model**: MiniMax-M3
+**Depends on**: 07 · **Parallel with**: 09, 10, 11 · **Blocks**: 12
+**Worktree**: `.agents/scripts/worktree.sh start 08 route-cards`
+
+## Goal
+
+The landing page's six chapter cards become one component over data.
+
+## Scope
+
+`src/components/blocks/RouteCard.astro`, `src/components/blocks/GridGroup.astro`.
+
+## Source
+
+`index.html` — six `<article class="card">` blocks differing only in number,
+title, summary, and href. Textbook extraction. Styles in `landing.css` +
+`chapters.css`.
+
+## Steps
+
+1. `GridGroup` from `.agents/templates/components/grid-group.astro`. Preserve
+   the `gap:1px` over a coloured parent separator technique — it is deliberate.
+2. `RouteCard` from `static-block.astro`: `number`, `title`, `summary`, `href`.
+3. Card content moves to the `chapters` collection, both locales.
+
+## Done when
+
+- [ ] Six cards render identically to `index.html` today
+- [ ] Screenshots at 560/800/1100/1600 match
+- [ ] Zero JS
+- [ ] `.agents/checklists/before-component.md` complete; `npm run gate` green
+
+## Do not
+
+Do not migrate `index.html` itself — that is task 12.