feat(exitstorm): add contact form + /api/contact worker

[arc-web]

Summary

• Adds a client-side contact form to the landing page (docs/index.html) that POSTs JSON to /api/contact.
• Adds the Cloudflare Worker exitstorm-api (workers/exitstorm-api/) implementing POST /api/contact → sends email via Cloudflare Email binding.
• Affected URL: https://exitstorm.com

Changes (2 commits)

1. feat(exitstorm): add contact form to landing page — docs/index.html
2. feat(exitstorm): add /api/contact email worker — workers/exitstorm-api/{package.json, src/index.js, wrangler.toml}

Checks + results

• pnpm check:site — PASS (exit 0: "Exitstorm site checks passed")
• worker dry run wrangler deploy --dry-run — PASS (exit 0; bindings: env.EMAIL, env.FROM_EMAIL, env.OWNER_EMAIL, env.ALLOWED_ORIGIN)
• pnpm build / pnpm typecheck / pnpm lint — BLOCKED locally: turbo: command not found because root pnpm install fails on better-sqlite3@11.10.0 native build under node v26.7.0 (V8 API incompatibility; pre-existing infra issue unrelated to this change — no TS/package files touched here).

Exclusions

• workers/exitstorm-api/.wrangler/cache/wrangler-account.json (generated account cache) is intentionally NOT committed. Explicit-path staging used; no .wrangler/cache anywhere in this PR.

Rollback

• Close this PR (no merge, no deploy, no branch deletion performed).