docs: correct Cursor Cloud setup notes (venv, backend pytest, lint)

[Cookie-Cat21]

Summary

Set up the development environment for Cloud Agents, validated it against the real backend (Neon Postgres + Groq + MPGS + Supabase), and corrected the ## Cursor Cloud specific instructions in AGENTS.md.

Secrets (DB/Groq/MPGS/Supabase keys) are written only to gitignored backend/.env and frontend/.env.local — never committed. This PR contains docs-only changes.

Docs changes

• Backend deps install into a venv at backend/.venv; run/test commands now activate it.
• Backend has pytest suites (41 tests) — replaced the stale "no unit tests" note; tests need pytest-asyncio + httpx.
• Accurate lint note: 2 react-hooks/set-state-in-effect errors + 6 no-img-element warnings.
• Added a Real-backend mode section: env-file wiring, Neon startup migrations, Groq streaming, and MPGS Demo Mode caveat.

Verification (real backend)

• ✅ GET /health/deep → database: ok, groq: configured (Neon migrations applied on startup).
• ✅ Groq streaming on /api/chat returns a live, loan-context LLM answer.
• ✅ Wallet transfer persisted 3 rows to the Neon transactions table (confirmed via direct query).
• ⚠️ MPGS /api/payments/session authenticates against the live Mastercard gateway but returns a gateway request-shape validation error; Demo Mode is the reliable card path.
• ✅ Backend pytest tests/ -v (41 passed), scripts/smoke.sh (13/13).
• ⚠️ Frontend npm run lint (2 pre-existing errors), ✅ npm run test:smoke, ✅ npm run dev.

Walkthrough — live Groq AI assistant

ceyfi_real_backend_groq_assistant_demo.mp4
Live Groq assistant loan response

Walkthrough — persona login + send money

ceyfi_persona_login_send_money_demo.mp4
Transfer success and updated remittance

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