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-05-content-guide.md

@@ -0,0 +1,38 @@
+# Task 05 — Guide content out of app.js
+
+**Agent**: `content-i18n-migrator` · **Model**: MiniMax-M3
+**Depends on**: 04 · **Parallel with**: 06 · **Blocks**: 15
+**Worktree**: `.agents/scripts/worktree.sh start 05 content-guide`
+
+## Goal
+
+Every `{ en, pt }` string in `app.js` lives in `src/content/guide/`, byte-identical.
+
+## Scope
+
+`src/content/guide/**`. Do **not** delete anything from `app.js` yet — task 15
+removes it once the page consumes the collection.
+
+## Steps
+
+1. `node .agents/scripts/extract-strings.mjs app.js > /tmp/before.json`
+   (~50 pairs across `phases`, `handsOnPrompts`, `modelGuide`, `skillSources`,
+   `skillInstallPrompts`).
+2. Move them into the collection. **Copy mechanically — never retype.** These
+   are hand-written translations with deliberate tone (`'Transforme ambiguidade
+   em trabalho'`); retyping introduces drift nobody catches until a Portuguese
+   speaker reads it.
+3. `node .agents/scripts/extract-strings.mjs src/content/guide/ > /tmp/after.json`
+4. `diff /tmp/before.json /tmp/after.json` → **must be empty**.
+
+## Watch for
+
+`handsOnPrompts` values are multi-line prompt strings built with `.join('\n')`.
+Preserve the exact line breaks and leading `-` bullets: they are copy-pasted by
+workshop attendees into an agent, and a mangled prompt breaks the exercise.
+
+## Done when
+
+- [ ] String diff empty
+- [ ] `astro check` passes; both locales present on every entry
+- [ ] `app.js` still untouched and the site still works