docs: add Scalattice OpenAI-compatible provider

[romulushill]

Summary

Adds a docs page for using Scalattice with aider via the OpenAI-compatible endpoint (https://api.scalattice.cloud/v1).

Create a key at https://scalattice.cloud/developers, then:

export OPENAI_API_BASE=https://api.scalattice.cloud/v1
export OPENAI_API_KEY=<slt_key>
aider --model openai/qwen-3-14b

Catalog IDs match GET https://api.scalattice.cloud/v1/models.

Test plan

• Page renders under Connecting to LLMs
• Install snippet and env vars match the other provider pages

[CLAassistant]

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