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/skills/content-migration/SKILL.md

@@ -0,0 +1,73 @@
+---
+name: content-migration
+description: Move bilingual copy out of app.js and catalog.js into typed Astro content collections without losing or altering a single string. Use for any task that relocates user-visible text.
+---
+
+# Content migration
+
+## What you are moving
+
+- `app.js` — ~50 `{ en, pt }` keys across `phases`, `handsOnPrompts`,
+  `modelGuide`, `skillSources`, `skillInstallPrompts`
+- `skills-review/catalog.js` + `submitted-catalog.js` — 24 entries with
+  `id`, `author`, `title`, `status`, `focus`, `wins[]`, `improve[]`, `extras`,
+  `improved` (full markdown)
+
+These are hand-written translations with deliberate tone. **Copy them. Never
+retype them.** Retyping introduces drift you will not notice.
+
+## Schema
+
+```ts
+// src/content/config.ts
+import { defineCollection, z } from 'astro:content';
+
+const localized = z.object({ en: z.string(), pt: z.string() });
+
+const guide = defineCollection({
+  type: 'data',
+  schema: z.object({
+    id: z.string(),
+    model: localized,
+    title: localized,
+    copy: localized,
+    code: localized,
+  }),
+});
+```
+
+Both locales **required**. A missing `pt` must be a build error — silent English
+fallback is how a bilingual site quietly becomes monolingual.
+
+## Procedure
+
+1. Extract the literals mechanically (script, not by hand).
+2. Write them into the collection.
+3. Diff extracted-before against extracted-after. Must be empty.
+
+```bash
+node .agents/scripts/extract-strings.mjs app.js          > /tmp/before.json
+node .agents/scripts/extract-strings.mjs src/content/    > /tmp/after.json
+diff /tmp/before.json /tmp/after.json
+```
+
+4. Only then delete the source literals.
+
+## The generator trap
+
+`skill-reviews/improved/**/SKILL.md` is **generated** from `catalog.js`
+`improved` fields by `scripts/build-skill-review.mjs`, and the output is
+committed to the repo. If you move `catalog.js`, that generator breaks silently
+— it will still run, just against nothing.
+
+Either keep the generator pointed at the new collection, or replace it and
+update `package.json`, `README.md`, `docs/operations-guide.md`, and the review
+desk footer, all of which reference it.
+
+## Markdown
+
+The `improved` fields are full Markdown rendered client-side today. Move them to
+real `.md` files in the collection and let Astro render at build time. That
+deletes the hand-rolled renderer and improves fidelity — but re-check the review
+desk's diff view, which compares original and improved source text and needs the
+raw string, not just rendered HTML.