docs: add product overview and engineering documentation

Document architecture, security, deployment, and development for contributors.

CONTEXT.md

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+# Pargar — domain summary
+
+> Full source of truth: [`docs/`](docs/README.md) · repo entry: [`README.md`](README.md)
+
+Gated LMS: verified watch → quiz with hearts → skill-tree unlock (staff) → mentor chat, events, weekly league, monthly XP challenges, certificates.
+
+## Stack (short)
+
+- **Backend:** Go (`backend/`) · Postgres · Redis · S3/RustFS · WS hub
+- **Frontend:** Next.js App Router · React Query · Tailwind · Vazirmatn FD
+- **Edge:** Traefik v3.7 — Compose and Helm/k3s
+
+## Student path (short)
+
+Login/CAPTCHA or register (public/invite) → `/cap` → `/player` → `/quiz` → staff unlock → certificate `/c/{publicId}` · profile `/profile` · hub `/unwrap`.
+
+Public password recovery is disabled for students; resets are admin-only. Browser sessions use HttpOnly cookies.
+
+## Docs
+
+| Topic | File |
+|-------|------|
+| Architecture | [docs/architecture.md](docs/architecture.md) |
+| Product | [docs/product.md](docs/product.md) |
+| Development | [docs/development.md](docs/development.md) |
+| Deployment | [docs/deployment.md](docs/deployment.md) |
+| Security | [docs/security.md](docs/security.md) |
+| Operations | [docs/operations.md](docs/operations.md) |
+| API | [docs/api.md](docs/api.md) |
+| Env | [docs/configuration.md](docs/configuration.md) |
+
+Phone registration, unlisted certificates, chat-export, rate limits, and production notes live in those docs (not duplicated here to avoid drift).