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-20-cutover.md

@@ -0,0 +1,58 @@
+# Task 20 — Cutover and cleanup
+
+**Agent**: `astro-architect`, **with a human watching** · **Model**: MiniMax-M3 assisting
+**Depends on**: all · **Worktree**: `.agents/scripts/worktree.sh start 20 cutover`
+
+This task touches production publishing. Do not run it unattended.
+
+## Goal
+
+The Astro build is what the world sees, the old files are gone, and the docs
+describe reality.
+
+## Steps
+
+1. **Full verification** on the built site: all 10 routes, all 6 query params,
+   both languages, vote widget against the live API, screenshots at four widths.
+2. **Delete the superseded files** — only after their replacements are proven:
+   `app.js`, `styles.css`, `responsive.css`, `chapters.css`, `landing.css`,
+   `rules/app.js`, `rules/styles.css`, `skills/app.js`, `skills/styles.css`,
+   `skills-review/*.js`, `skills-review/*.css`, and the ten old `index.html`
+   files. `git rm`, one commit, reviewable.
+   **Keep**: `hands-on/**` (now under `public/`), `submitted-skills/**`,
+   `skill-reviews/**`, `docs/**`, `vote-service/**`.
+3. **Publish** via the mechanism chosen in task 01.
+4. **Verify on the real host** with a cache-buster:
+   ```bash
+   for r in "" full-guide summary models agents skills rules skills-review \
+            hands-on/starter hands-on/rules; do
+     curl -sS -o /dev/null -w "%{http_code} $r\n" \
+       "https://netcracker.pages.marcospaulo.dev.br/ai-for-dummies/$r/?v=$(git rev-parse --short HEAD)"
+   done
+   ```
+   All ten must be 200. A stale cached 200 looks identical to success — the
+   `?v=` is what distinguishes them.
+5. **Update the docs**: `README.md`, `docs/operations-guide.md` (build + publish
+   path, and it must stop claiming `pages` is "the exact published source" if
+   that is no longer true), `GATES.md`, and `AGENTS.md` (stack is no longer
+   "migration in progress").
+6. **Fast-forward `pages`** per the procedure in `docs/operations-guide.md`.
+
+## Rollback
+
+`pages` still holds the working vanilla site until you overwrite it. If cutover
+fails, reset `pages` to its previous commit — the old site returns immediately.
+Note the SHA before you start:
+
+```bash
+git rev-parse origin/pages   # write it down
+```
+
+## Done when
+
+- [ ] Ten routes 200 on the real host with a fresh cache-buster
+- [ ] Vote widget works end-to-end from the published origin (CORS is
+      origin-sensitive — `ALLOWED_ORIGIN` must still match)
+- [ ] Old files deleted; `npm run gate` green
+- [ ] Docs match reality
+- [ ] Previous `pages` SHA recorded for rollback