Document the TypeScript SDK's Sandbox support

[mmilutinovic371]

Summary

• Adds a TypeScript SDK section to the Sandboxes page, mirroring the existing Python SDK section — install, quickstart, try/finally/await using cleanup, large-script pattern, and error types.
• Verified against the actual API surface in deepinfra/deepinfra-node#67 (merged into that repo's main), not guessed — method names, option shapes, duration parsing, and exception classes all read from the real diff.
• Cross-links the new section from the page intro and the plan-catalog bullet, and updates the client-side-exceptions sentence to cover both SDKs since they share identical class names.

Note: deepinfra-node#67 is merged but the deepinfra npm package hasn't been re-published since (still 2.0.2, from 2024-05-08) — npm install deepinfra in this doc assumes that release lands.

Test plan

• Reviewed rendered Mintlify structure (headings, code blocks)
• Cross-checked SDK method names/signatures against the merged deepinfra-node PR diff