Initialize monorepo: core packages, adapters, templates, apps, tooling, and CI

[saurabhsharma2u]

Motivation

• Establish a monorepo scaffold for the og-engine project including core runtime, platform adapters, templates, and example apps to enable multi-target development.
• Provide shared types and runtime contracts to standardize template rendering and platform integrations.
• Add developer tooling and workspace configuration to enforce consistent linting, formatting, typechecking, and CI.
• Prepare CI and security scan workflows to validate builds and templates on PRs.

Description

• Add workspace and package metadata: pnpm-workspace.yaml, package.json, pnpm-lock.yaml, turbo.json, and base TypeScript config tsconfig.base.json.
• Introduce packages: @og-engine/types (shared types), @og-engine/core (render + handler + wasm stubs + fonts + params + cache-key), @og-engine/sandbox (sandboxed render), and adapters @og-engine/adapter-node, @og-engine/adapter-cloudflare, and @og-engine/adapter-vercel with concrete storage/cache/registry implementations.
• Add apps: apps/server-node, apps/web, and apps/worker-cf with simple health routes and environment defaults.
• Add templates: templates/dark, templates/minimal, templates/sunset, and base helpers with previews and metadata.
• Add developer tooling and CI: eslint.config.mjs, .prettierrc, .gitattributes, .gitignore, Husky pre-commit hook, lint-staged configuration, scripts/scan-template.mjs, and GitHub Actions workflows ci.yml and template-scan.yml that run pnpm install, pnpm typecheck, pnpm lint, pnpm test, and pnpm build.

Testing

• CI workflow added to run pnpm install --frozen-lockfile, pnpm typecheck, pnpm lint, pnpm test, and pnpm build for pushes and PRs.
• Most packages include a placeholder test script that prints no tests, so there are currently no unit tests exercised by pnpm test.
• Typecheck and lint scripts are configured in each package and will be executed by the CI pipeline once run.
• No CI runs were included in this change; the PR only adds the configuration required to run the automated checks on future CI runs.

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Codex Task