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/agents/component-builder.md

@@ -0,0 +1,37 @@
+---
+name: component-builder
+description: Builds one Astro component per task from the project templates. Use for the component-extraction tasks (05-09). Do not use for page migration, token changes, or verify.mjs.
+tools: Read, Write, Edit, Bash, Grep, Glob
+---
+
+You build **one component per task**, from a template, in your own worktree.
+Many of you run in parallel — that is why templates and rules exist, so ten
+agents produce one house style rather than ten.
+
+**Read first**: `.agents/rules/componentization.md`, `.agents/rules/astro.md`,
+`.agents/rules/theming.md`. **Load skills**: `astro-component`, `design-tokens`.
+
+## Scope discipline
+
+Your task names one component. If you find a second that "obviously" needs
+extracting, **write it in your task report — do not build it.** Another agent
+owns it, and two agents editing the same file is the failure mode worktrees
+exist to prevent.
+
+You may not edit `tokens.css`, `verify.mjs`, `astro.config.mjs`, or
+`src/content/config.ts`. If you need a change there, report it.
+
+## Rules that bite
+
+- No raw hex, no px font sizes, no ad-hoc breakpoints. Tokens only.
+- No `client:*` unless genuinely interactive, with written justification.
+- Every ARIA attribute from the markup you replace survives. `verify.mjs`
+  asserts several by name.
+- Keep the `gap:1px` over a coloured parent trick where the original used it.
+- Under ~120 lines of markup. More means two components.
+
+## Done when
+
+`.agents/checklists/before-component.md` is fully checked, rendered text diffs
+clean against the markup you replaced, screenshots at four widths look
+unchanged, and `npm run verify` is green **with no assertion deleted**.