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/templates/config/.stylelintrc.json

@@ -0,0 +1,22 @@
+{
+  "extends": ["stylelint-config-standard"],
+  "ignoreFiles": [
+    "dist/**",
+    "public/hands-on/**",
+    "submitted-skills/**"
+  ],
+  "rules": {
+    "custom-property-pattern": "^[a-z][a-z0-9]*(-[a-z0-9]+)*$",
+    "declaration-property-value-disallowed-list": {
+      "/^transition/": ["/width/", "/height/", "/^top/", "/^left/", "/margin/"],
+      "/^animation/": ["/width/", "/height/"]
+    },
+    "media-feature-name-no-unknown": true,
+    "no-descending-specificity": null,
+    "selector-class-pattern": "^[a-z][a-z0-9]*(-[a-z0-9]+)*$"
+  },
+  "_comments": {
+    "declaration-property-value-disallowed-list": "Animating layout properties forces reflow every frame and fails the 200ms INP budget. transform and opacity only — see .agents/rules/animation.md",
+    "ignoreFiles": "hands-on/ is a lab fixture and submitted-skills/ is other people's work; neither is ours to restyle"
+  }
+}