docs: add CLOUD.md for cloud agent development guidance

Co-authored-by: Vikhyath Mondreti <icecrasher321@users.noreply.github.com>

.cursor/CLOUD.md

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+# Sim Cloud Agent Guide
+
+## Project Overview
+
+Sim is an AI agent workflow builder. Turborepo monorepo with Bun workspaces.
+
+### Services
+
+| Service | Port | Command |
+|---------|------|---------|
+| Next.js App | 3000 | `bun run dev` (from root) |
+| Realtime Socket Server | 3002 | `cd apps/sim && bun run dev:sockets` |
+| Both together | 3000+3002 | `bun run dev:full` (from root) |
+| Docs site | 3001 | `cd apps/docs && bun run dev` |
+| PostgreSQL (pgvector) | 5432 | Docker container `simstudio-db` |
+
+## Common Commands
+
+- **Lint**: `bun run lint:check` (read-only) or `bun run lint` (auto-fix)
+- **Format**: `bun run format:check` (read-only) or `bun run format` (auto-fix)
+- **Test**: `bun run test` (all packages via turborepo)
+- **Test single app**: `cd apps/sim && bunx vitest run`
+- **Type check**: `bun run type-check`
+- **Dev**: `bun run dev:full` (Next.js app + realtime socket server)
+- **DB migrations**: `cd packages/db && bunx drizzle-kit migrate --config=./drizzle.config.ts`
+
+## Architecture Notes
+
+- Package manager is **bun** (not npm/npx). Use `bun` and `bunx`.
+- Linter/formatter is **Biome** (not ESLint/Prettier).
+- Testing framework is **Vitest** with `@sim/testing` for shared mocks/factories.
+- Database uses **Drizzle ORM** with PostgreSQL + pgvector.
+- Auth is **Better Auth** (session cookies).
+- Pre-commit hook runs `bunx lint-staged` which applies `biome check --write`.
+- `.npmrc` has `ignore-scripts=true`.
+- Docs app requires `fumadocs-mdx` generation before type-check (`bunx fumadocs-mdx` in `apps/docs/`).
+- Coding guidelines are in `CLAUDE.md` (root) and `.cursor/rules/*.mdc`.
+- See `.github/CONTRIBUTING.md` for contribution workflow details.