Introduce typed PLATFORM_SIZES, improved font/WASM pipeline, API param parsing, UI refresh, and workspace reorg

[saurabhsharma2u]

Motivation

• Provide a single source of truth for platform output sizes and stronger typing across the stack to avoid mismatched size/format values.
• Make the core rendering pipeline more robust: better font loading with fallbacks, deterministic cache keys, and runtime-aware WASM initialization.
• Harden request handling in adapters/servers by validating and coercing query params and formats.
• Refresh the web UI and reorganize internal packages (sandbox -> internal-sandbox) to align with the updated core contracts.

Description

• Add a new @og-engine/types package (canonical PLATFORM_SIZES, PlatformSize, request/template contracts) and update consumers to use typed sizes.
• Update server/adapters (apps/server-node, apps/web, apps/worker-cf) to parse and coerce size and format query params with safe defaults and stricter template validation.
• Refactor @og-engine/core: add docs/comments, move sandbox dependency to internal/sandbox, implement buildCacheKey, runtime-aware initWasm/getResvg, improved fonts.ts with Google Fonts CSS discovery, CDN and local fallbacks, and typed handler/render interfaces (RenderResult, handler response shapes).
• Adjust rendering pipeline to use the renamed internal-sandbox in render.ts, and make pre-generation/background generation robust and properly referenced.
• Update Next.js app: new global styles (globals.css), site layout (layout.tsx) and home/preview pages for a refreshed UI/UX and async preview route handling.
• Update templates (dark, minimal, sunset) with redesigned metadata, schemas and render implementations, remove in-repo binary preview PNGs from the repo and add .gitignore rule for generated previews.
• Workspace/tooling changes: rename packages/sandbox -> internal/sandbox, update references in packages/core and lockfile, update pnpm-workspace.yaml, and change turbo.json schema/tasks.

Testing

• Ran a monorepo build with pnpm -w -s build, which completed successfully.
• Performed TypeScript checks with pnpm -w -s typecheck, which passed without type errors.
• There are no unit test suites in the affected packages (most test scripts are placeholders returning "no tests").

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Codex Task