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-15-page-full-guide.md

@@ -0,0 +1,62 @@
+# Task 15 — Full guide
+
+**Agent**: `page-migrator` · **Model**: **Codex** — hardest task in the plan
+**Depends on**: 05, 10, 13 · **Parallel with**: 16
+**Worktree**: `.agents/scripts/worktree.sh start 15 page-full-guide`
+
+## Goal
+
+`/full-guide/` → Astro. 22 KB of HTML, a 50 KB script, 30 KB of CSS, twelve
+render functions, bilingual throughout.
+
+## What `app.js` actually is
+
+Not application code — a **bilingual content database** (task 05 already moved
+it) plus ~12 `render*` functions that swap `innerHTML` on tab clicks. Once
+content is a collection, the remaining JS is small: tab state and a language
+toggle.
+
+## Islands
+
+Only these hydrate. Everything else is server-rendered.
+
+| Island | Directive | Why |
+| --- | --- | --- |
+| Phase tabs | `client:visible` | click-driven panel swap |
+| Tree / worker / route / model / effort / skill selectors | `client:visible` | same pattern; consider one generic selector island |
+| Language toggle | `client:idle` | page-wide, not urgent |
+| Copy-prompt buttons | `client:visible` | clipboard |
+
+If you end up with 12 separate islands you have missed the pattern — they are
+one selector component with different data.
+
+## Asserted by verify.mjs — all must survive
+
+`const phases`, `const handsOnPrompts`, `const modelGuide`, `const skillSources`,
+`const skillInstallPrompts`, `render('plan')`, `renderTree`, `renderWorker`,
+`renderRoute`, `renderModelProvider`, `renderEffort`, `renderSkillFile`,
+`renderSkillWorkflow`, `renderCommonSkill`, `renderHandsOn`, `copyPrompt`.
+
+These are **implementation-detail assertions** — they look deletable and are
+not. Each pins a feature. Coordinate with task 19 to replace each with an
+output-level assertion of the same behaviour. **Never delete one yourself.**
+
+Also: `data-copy-target="prompt-install-skills|prompt-basic|prompt-skills"`,
+`hands-on/starter/`, `additional-reading.md`, `role="tablist"`, `<table>`.
+
+## Watch for
+
+- `copyPrompt` uses `navigator.clipboard` with a `document.execCommand`
+  fallback. Keep both — the fallback exists for non-secure contexts.
+- The hands-on prompt strings are copy-pasted by attendees into an agent.
+  Exact whitespace and line breaks matter.
+- `responsive.css` (30 KB) mostly serves this page. Port what is needed, prove
+  the rest dead, delete it. Screenshots are the proof.
+
+## Done when
+
+- [ ] Snapshot diff empty
+- [ ] Every interaction works: all tabs, both languages, all copy buttons
+- [ ] Keyboard: arrow keys move between tabs; focus visible throughout
+- [ ] JS payload **smaller** than today's 50 KB (content is now static)
+- [ ] Screenshots match at four widths; checklist complete; `npm run gate` green