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/scripts/install-claude-agents.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+# `.agents/` is the vendor-neutral home for this project's rules, skills, and
+# agent definitions — MiniMax, Gemini, and Codex all read plain files from it.
+#
+# Claude Code, however, discovers subagents and skills at fixed paths. This
+# symlinks them so there is exactly ONE copy of every definition and no drift.
+#
+#   .agents/scripts/install-claude-agents.sh
+set -euo pipefail
+
+root="$(git rev-parse --show-toplevel)"
+cd "$root"
+
+mkdir -p .claude
+
+for target in agents skills; do
+  link=".claude/$target"
+  if [ -e "$link" ] && [ ! -L "$link" ]; then
+    echo "refusing: $link exists and is not a symlink — move it aside first" >&2
+    exit 1
+  fi
+  ln -sfn "../.agents/$target" "$link"
+  echo "linked $link -> .agents/$target"
+done
+
+echo
+echo "Claude Code will now load:"
+ls -1 .agents/agents/*.md | sed 's|.*/|  agent: |;s|\.md$||'
+ls -1d .agents/skills/*/  | sed 's|.*/skills/|  skill: |;s|/$||'