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/templates/config/eslint.config.js

@@ -0,0 +1,26 @@
+// Flat config (ESLint 9+). Copy to the repository root in task 01.
+import js from '@eslint/js';
+import astro from 'eslint-plugin-astro';
+
+export default [
+  js.configs.recommended,
+  ...astro.configs.recommended,
+  {
+    ignores: [
+      'dist/**',
+      'public/hands-on/**',   // lab fixtures ship verbatim — linting them would
+                              // invite "fixes" that break the exercise
+      'submitted-skills/**',  // other people's work, reproduced as submitted
+      'skill-reviews/**',     // generated from skills-review/catalog.js
+      'vote-service/**',      // Go service, separate lifecycle
+    ],
+  },
+  {
+    rules: {
+      'no-console': ['warn', { allow: ['warn', 'error'] }],
+      eqeqeq: ['error', 'always'],
+      'no-var': 'error',
+      'prefer-const': 'error',
+    },
+  },
+];