chore(api-nodes): add upload_image_to_comfyapi to make code look better

[bigcat88]

PR adds a new upload_image_to_comfyapi() function that simplifies the common single-image upload pattern in API nodes.

Before:

url = (await upload_images_to_comfyapi(cls, image, max_images=1))[0]

After:

url = await upload_image_to_comfyapi(cls, image)

This mirrors the existing upload_video_to_comfyapi and upload_audio_to_comfyapi helpers which also return a single URL string.

API Node PR Checklist

Scope

• Is API Node Change

Pricing & Billing

• Need pricing update
• No pricing update

If Need pricing update:

• Metronome rate cards updated
• Auto‑billing tests updated and passing

QA

• QA done
• QA not required

Comms

• Informed Kosinkadink