Set up FRAGLINE dev environment + add Cursor Cloud instructions

[P4ND4907]

Summary

• Set up the development environment for the FRAGLINE app (React + TypeScript + Vite, in fragline/).
• Added AGENTS.md with a ## Cursor Cloud specific instructions section documenting that the app lives in fragline/, the lint/build/dev/preview commands, Node version requirement, and the localStorage-based state caveat.
• Registered a minimal, idempotent update script for future cloud sessions: [ -f fragline/package.json ] && npm install --prefix fragline.

No application code was changed.

Testing

• cd fragline && npm install — installed 34 packages, 0 vulnerabilities.
• cd fragline && npm run lint (oxlint) — passes (only a pre-existing no-unused-vars warning in scripts/stuck-feed.mts).
• cd fragline && npm run build (tsc -b + vite build) — builds successfully.
• cd fragline && npm run dev — Vite dev server serves at http://localhost:5173 (HTTP 200).
• End-to-end manual test in the browser: idle income accrues, purchased a Power team upgrade (cash deducted, level up), navigated Match/Squad/Market/Career, signed a player from the transfer market, and trained the Aim skill. No console errors.

Safety Checklist

• I did not commit secrets, tokens, passwords, .env files, generated credentials, private exports, build outputs, or dependency folders.
• Real-money, production, account-writing, device-writing, destructive, and message-sending behavior remains disabled by default.
• Risky actions require an explicit user confirmation, dry run, sandbox, paper mode, or local-only path.
• Logs, screenshots, fixtures, and examples do not expose private user/customer data.
• Setup, environment, and rollback notes are updated when needed.