docs: add FutureInfra AI endpoint guide

[uxidev]

Summary

Adds a FutureInfra custom endpoint guide under the LibreChat YAML AI endpoints docs, following the format of the NEAR AI Cloud and OpenRouter pages. FutureInfra's AI router is OpenAI-compatible and serves 300+ models with vendor/model ids.

The example uses:

• FUTUREINFRA_API_KEY
• https://futureinfra.ai/v1/ai
• openai/gpt-4o-mini and anthropic/claude-sonnet-4 as the default models
• models.fetch: true so LibreChat loads the live list from /v1/ai/models

Also adds a monochrome FutureInfra provider icon and the sidebar entry in meta.json.

Testing

• prettier --check on the changed files
• curl -fsSL https://futureinfra.ai/v1/ai/models | jq -e '.data | map(.id) | contains(["openai/gpt-4o-mini", "anthropic/claude-sonnet-4"])'

🤖 Generated with Claude Code

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