### What problem does this PR solve?
Add a Go driver for **n1n.ai** (https://docs.n1n.ai), one of the
unchecked providers on the umbrella tracking issue #14736. n1n.ai is an
OpenAI-compatible aggregator hosting a 450+ model catalog (GPT, Claude,
Gemini, DeepSeek, Kimi, Qwen, embedding + reranker families) under
`https://api.n1n.ai/v1`.
Until this PR, a tenant who configured `n1n` as a model provider in the
Go layer fell through to the default branch of
`internal/entity/models/factory.go` and got the dummy driver.
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Co-authored-by: sxxtony <sxxtony@users.noreply.github.com>
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