QVAC-11724 feat[api]: implement cancel embed operation

[simon-iribarren]

Note: be concise and prefer bullet points.

🎯 What problem does this PR solve?

• No way to cancel an in-flight embed() call — users had to wait for the full embedding to complete even if it was no longer needed.

📝 How does it solve it?

• Adds operation: "embeddings" as a new variant of the cancel() API.
• Routes through the same bare cancel() path as operation: "inference", calling model.addon.cancel() on the embedding model.
• Delegation support added for cases where the embedding model is served by a remote peer.

🔌 API Changes

// Cancel an in-flight embed call
void embed({ modelId, text });
await new Promise(resolve => setTimeout(resolve, 1000));
await cancel({ operation: "embeddings", modelId });

[gianni-cor]

the addon already has the cancel method. are you using that?

[github-actions]

Tier-based Approval Status

**PR Tier:** TIER1

**Current Status:** ✅ APPROVED

**Requirements:**
- 1 Team Member approval ✅ (1/1)
- 1 Team Lead OR Management approval ✅ (1/1)



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*This comment is automatically updated when reviews change.*

[simon-iribarren]

/review