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-04-content-schema.md

@@ -0,0 +1,37 @@
+# Task 04 — Content collection schema
+
+**Agent**: `content-i18n-migrator` · **Model**: MiniMax-M3
+**Depends on**: 01 · **Parallel with**: 02, 03 · **Blocks**: 05, 06
+**Worktree**: `.agents/scripts/worktree.sh start 04 content-schema`
+
+## Goal
+
+Typed collections that make a missing translation a build error.
+
+## Scope
+
+`src/content/config.ts` only. You own it.
+
+## Steps
+
+1. Define `const localized = z.object({ en: z.string(), pt: z.string() })`.
+   **Both required.** A missing `pt` must fail the build — silent English
+   fallback is how bilingual sites quietly become monolingual.
+2. Collections:
+   - `guide` — `phases`, `modelGuide`, `skillSources`, `handsOnPrompts`, `skillInstallPrompts` from `app.js`
+   - `chapters` — copy for `/models/`, `/agents/`, `/skills/`, `/summary/`
+   - `reviews` — the 24 entries: `id`, `author`, `title`, `status`, `focus`, `wins[]`, `improve[]`, `extras`, `improved`
+3. **Make the language-switching decision** and record it here:
+   - *client-side swap* — matches today, no URL change, both languages in the payload. **Recommended.**
+   - *route-based `/en/` `/pt/`* — better SEO, changes every existing URL, needs redirects.
+
+## Done when
+
+- [ ] `astro check` passes
+- [ ] A deliberately missing `pt` field fails the build (prove it, then revert)
+- [ ] The language decision is written down here with its reason
+
+## Do not
+
+Do not move any content yet. Schema only — tasks 05 and 06 fill it, and they
+run in parallel against the shape you define.