feat: bootstrap contactkit monorepo

[Copilot]

Implements the full @contactkit/server and @contactkit/client spec from scratch on top of the existing scaffold.

Server (@contactkit/server)

• Env — Renamed vars to spec (EMAIL_PROVIDER, MAIL_TO, MAIL_FROM, MAIL_SUBJECT_PREFIX, ALLOWED_ORIGINS, RATE_LIMIT_MAX, RATE_LIMIT_WINDOW, LOG_LEVEL); fail-fast conditional validation (resend requires RESEND_API_KEY, smtp requires SMTP_HOST+SMTP_PORT)
• Mailer interface — send() now accepts replyTo and returns Promise<{ id?: string }>; both ResendMailer and SmtpMailer updated accordingly; replyTo set to submitter's email on every send
• POST /contact — Added subject field; honeypot (website) checked pre-schema to silently return { ok: true, id } without leaking 400; Turnstile failure returns 403; response always includes a message id (provider id or crypto.randomUUID())
• GET /health — Returns { status, uptime } (uptime in seconds since server start)
• GET / — New endpoint returning { name, version } from package.json
• server.ts — 16 KB body limit; trustProxy: true (Railway); rate limiting and log level wired from env
• Dockerfile — Multi-stage build; pnpm via corepack; non-root runtime user

Client (@contactkit/client)

• ContactClient (renamed from ContactKitClient) — send() method (was submit()); subject field; timeoutMs option (default 10 s); fetch option (was fetchFn)
• ContactError (renamed from ContactKitError) — Exposes status: number and code: ContactErrorCode; status-to-code mapping: 400→validation, 403→captcha_failed, 429→rate_limited, 5xx→server

import { ContactClient, ContactError } from '@contactkit/client';

const client = new ContactClient({ baseUrl: 'https://contact.example.com', timeoutMs: 10_000 });

try {
  const { id } = await client.send({ name: 'Jane', email: 'jane@example.com', message: 'Hi' });
} catch (err) {
  if (err instanceof ContactError) console.error(err.code, err.status); // e.g. "rate_limited" 429
}

Tests & tooling

• Server tests — env validation (missing MAIL_TO, missing provider creds), GET /, GET /health, valid contact (mailer called, id returned), subject+replyTo forwarding, invalid payload 400, honeypot silent 200, rate limit 429
• Client tests — success path, error code mapping (400/429/403), NetworkError, AbortError → timeout
• CI — Added tsc --noEmit typecheck step before lint
• .env.example and README updated to reflect new env var names, provider setup, and self-host notes