docs(config): document switchyard and litellm native auto-routing

[yanaSelin]

Summary

Documents two independent, admin-facing LLM auto-routing mechanisms in AI/Run CodeMie's model configuration:

• Switchyard — per-call tier routing between a capable and a cost-efficient model (signal / classifier modes)
• LiteLLM native auto-routing recognition — how CodeMie recognizes a LiteLLM-side auto-router via litellm_router, so it is not misconfigured as a normal deployment or chained with a Switchyard router

Changes

• New: docs/admin/configuration/codemie/ai-models-integration/switchyard-model-routing.md — YAML router schema, tuning parameters, model dropdown effect, response headers
• New: docs/admin/configuration/codemie/ai-models-integration/litellm-native-auto-routing.md — litellm_router declaration in LiteLLM's model_info, kept as a separate, alternative mechanism (not part of Switchyard)
• Updated sidebars.ts, api-configuration.md, ai-models-integration/index.md, codemie-native-llm-config.md, extensions/litellm-proxy/model-configuration.md (terse switchyard/litellm_router field entries, linking out to avoid duplication), and user-guide/assistants/chat-input-settings.md (end-user note on SY-prefixed model entries)
• New FAQ entries: faq/what-is-switchyard-auto-routing-in-codemie.md, faq/how-do-i-configure-a-switchyard-router-for-a-model.md

Testing

• Tested locally with npm start
• All pages render correctly
• Images display properly (n/a — no images added)
• Internal links work
• Sidebar navigation works

Quality Checks

• npm run check passes (typecheck + lint + commitlint)
• No MDX compilation errors
• No raw angle brackets (<text> must be `<text>`)
• Sidebar references document IDs (not filenames)
• Images stored locally next to content (not in static/img/)
• Commit messages follow Conventional Commits
• No secrets or credentials in documentation

Additional Notes

Content is based on the currently open MR epm-cdme/codemie!4241 ("Migrate to official Switchyard and introduce a Router abstraction"). The litellm_router recognition via LiteLLM's model_info block depends on a parsing fix planned for that same MR — the current merged code only reads litellm_router from CodeMie's native config, not from a live-synced LiteLLM catalog.

[github-actions]

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