♻️ Support Deno 2 Response typing

[AnandChowdhary]

Summary

• Copy generated GIF bytes into an ArrayBuffer-backed Uint8Array before constructing the HTTP response.
• Restores type-checking under Deno 2 while preserving the Deno 1 CI contract and HEAD behavior.

Validation

• deno test --allow-run --allow-net --allow-read (Deno 2.9.0)
• deno test --allow-read (Deno 1.46.3, matching the v1 CI line)
• Focused Deno lint/format checks, GIF/HEAD response probe, diff check, and independent staged-diff review.