add AI21 Labs Provider

[MykolaBiron]

Adds AI21 Labs as a provider with their two current models, Jamba Large and Jamba Mini.

Pricing verified against https://www.ai21.com/pricing
Context window and release snapshots verified against https://docs.ai21.com/docs/jamba-foundation-models
Uses @ai-sdk/openai-compatible since AI21 has no dedicated AI SDK package; endpoint is OpenAI-shaped (POST /studio/v1/chat/completions)

[github-actions]

Action items

• [high] [violation] providers/ai21/logo.svg:1 - Check: New provider logo.svg must use currentColor, have no fixed width/height, and preferably a square viewBox. Why: The logo still sets height="1em" and inline style, and uses a wide wordmark viewBox="0 0 103 24", so it does not meet the new-provider logo requirements and will scale poorly as a provider icon. Check: AGENTS.md / README logo rules. Action: Replace with a clean mark-only SVG: fill="currentColor" (or path fills), no width/height/style, no hardcoded colors, and preferably a square viewBox (e.g. 0 0 24 24).

[github-actions]

No actionable findings.