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/scripts/snapshot-route.mjs

@@ -0,0 +1,37 @@
+#!/usr/bin/env node
+// Rendered-text snapshot of one route. This is the migration's regression net:
+// token matching in verify.mjs cannot catch a dropped paragraph, this can.
+//
+// Usage:
+//   node .agents/scripts/snapshot-route.mjs http://localhost:4173/models/
+//   node .agents/scripts/snapshot-route.mjs dist/models/index.html
+//
+// Take a snapshot from the vanilla site BEFORE migrating, then diff the built
+// output against it. An empty diff is the proof that nothing was lost.
+
+import { readFileSync } from 'node:fs';
+
+const target = process.argv[2];
+if (!target) {
+  console.error('usage: snapshot-route.mjs <url|path>');
+  process.exit(2);
+}
+
+const html = target.startsWith('http')
+  ? await (await fetch(target)).text()
+  : readFileSync(target, 'utf8');
+
+const text = html
+  // Drop anything that is not user-visible prose.
+  .replace(/<script[\s\S]*?<\/script>/gi, '')
+  .replace(/<style[\s\S]*?<\/style>/gi, '')
+  .replace(/<!--[\s\S]*?-->/g, '')
+  .replace(/<[^>]+>/g, '\n')
+  .replace(/&amp;/g, '&').replace(/&lt;/g, '<').replace(/&gt;/g, '>')
+  .replace(/&quot;/g, '"').replace(/&#0?39;/g, "'").replace(/&nbsp;/g, ' ')
+  .split('\n')
+  .map((line) => line.trim())
+  .filter(Boolean)
+  .join('\n');
+
+console.log(text);