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/rules/code-style.md

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+# Rule: code style
+
+## Match what is there
+
+This codebase has a real voice: dense one-liner CSS, terse ES modules, comments
+that explain *why* and never *what*. Do not reformat it into someone else's
+house style as a side effect of a task.
+
+The one exception is CSS minification-by-hand — `styles.css` is single-line and
+unreadable. Component `<style>` blocks should be normally formatted. That is an
+improvement, not a style disagreement.
+
+## Comments
+
+Write the comment that stops the next person from making a mistake. The existing
+codebase does this well:
+
+```js
+// The cluster's nginx ingress runs with `use-forwarded-headers` off, so it
+// *overwrites* X-Forwarded-For with its own downstream peer — the VPS's
+// tailnet address — which would collapse every visitor into a single voter.
+```
+
+That comment earns its place. `// set the colour` does not.
+
+## Naming
+
+- Components `PascalCase.astro`; everything else `kebab-case`.
+- Booleans read as assertions: `isOpen`, `hasVoted`, not `open`, `voted`.
+- No abbreviations that are not already in the codebase's vocabulary.
+
+## TypeScript
+
+Astro brings TS. Use it: typed props, typed collections, `strict` on. Never
+`any` — if the type is genuinely unknown, `unknown` plus a narrow.
+
+## Dead code
+
+Delete it. Do not comment it out, do not leave it behind a flag. Git remembers.
+
+This matters here specifically: `responsive.css` is 30 KB of accumulated
+overrides, and the temptation during migration will be to port it wholesale
+"just in case". Prove each rule is needed or drop it.
+
+## Commits
+
+Present tense, lowercase, `type: subject`, matching the existing log
+(`feat:`, `fix:`, `docs:`). The body explains why, and states what you did not do.