docs: add Kyma API community provider

[sonpiaz]

Summary

Adds Kyma API as a community provider for the Vercel AI SDK.

Package: @kyma-api/ai-sdk — published on npm

What is Kyma API?
Kyma API is an OpenAI-compatible LLM gateway that serves 20+ open-source models (DeepSeek V3/R1, Qwen 3.6 Plus, Llama 3.3 70B, Gemma 4, Gemini 2.5 Flash, Kimi K2.5, MiniMax M2.5, and more) through a single endpoint. It includes:

• Free credits on signup
• Smart model aliases (best, fast, code, reasoning, vision, long-context)
• 4-layer fallback routing for reliability
• OpenAI-compatible API at https://kymaapi.com/v1

Implementation: Uses @ai-sdk/openai-compatible as the base — no custom protocol code.

import { kyma } from '@kyma-api/ai-sdk';
import { generateText } from 'ai';

const { text } = await generateText({
  model: kyma('deepseek-v3'),
  prompt: 'Explain quantum computing simply.',
});

Checklist

• npm package published: https://www.npmjs.com/package/@kyma-api/ai-sdk
• Uses @ai-sdk/openai-compatible as base
• Follows existing MDX doc format
• Model capabilities table included
• Setup instructions with pnpm/npm/yarn/bun tabs