feat(ai): add Azure AI Foundry provider

[Taitranz]

Summary

• Adds @effect/ai-azure-foundry — Azure AI Foundry provider targeting the v1 API (OpenAI-compatible)
• Reuses Generated.ts types and ResponseStreamEvent from @effect/ai-openai with a standalone language model implementation
• Supports Azure-specific api-key header auth, Entra ID token refresh via tokenProvider, resource-scoped base URLs, optional api-version for classic API fallback, and Azure content filter metadata

Split from #6165 per @IMax153's request to target v4.

Test plan

• Verify package builds successfully
• Verify language model implementation works against Azure AI Foundry API
• Verify streaming responses with Azure content filter metadata

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Latest commit: 8ccb258

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