docs: Update Inception provider docs to include mercury-2 model

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Summary

The Inception provider documentation at docs/customize/model-providers/top-level/inception.mdx needs to be updated to include the newly added mercury-2 model.

Related PR

• feat: add Inception Labs mercury-2 model #12156 - feat: add Inception Labs mercury-2 model

What needs to be documented

• mercury-2 model (128k context, tool support, OpenAI-compatible)
• mercury-edit-2 and mercury-coder-small models
• Tool calling capability with mercury-2
• Dynamic model fetching support via OpenAI listModels()

Example configuration

models:
  - name: Mercury 2
    provider: inception
    model: mercury-2
    apiKey: <INCEPTION_API_KEY>

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Co-Authored-By: Continue noreply@continue.dev
Co-authored-by: bekahhw rhawrot@gmail.com