Docs: Update Inception provider docs with mercury-2 model details

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Summary

PR #12156 added the Inception Labs mercury-2 model with 128k context and tool calling support, but the Inception provider documentation doesn't include specific model details.

Current State

• docs/customize/model-providers/top-level/inception.mdx exists but uses generic placeholders like <MODEL_NAME> and <MODEL_ID>
• No mention of specific available models (mercury-2, mercury-edit-2, mercury-coder-small)
• No mention of tool calling support for mercury-2

Documentation Needed

1. Add a section listing available Inception models with their capabilities:
   • mercury-2: 128k context, tool calling support
   • mercury-edit-2
   • mercury-coder-small
2. Update the configuration example to show a concrete model (e.g., mercury-2)
3. Mention tool calling capabilities where relevant

Related PR

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

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