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>

.husky/pre-commit

@@ -0,0 +1,10 @@
+# Tier 1: staged files only. Budget < 3s — see .agents/rules/gates.md
+#
+# Husky v9+: no `husky.sh` sourcing (deprecated in v9, removed in v10).
+
+# Guard the silent-failure mode: if hooks are configured but .husky/_ is
+# missing (fresh worktree that never ran `npm install`), this file would not
+# execute at all. Nothing we can do from inside it — so verify-hooks.sh exists
+# and worktree.sh runs it at creation time.
+
+npx --no-install lint-staged