feat: add custom reranker provider support in web search config

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Summary

• Add CUSTOM to RerankerTypes enum in data-provider config
• Add customRerankerApiUrl, customRerankerApiKey, customRerankerModel fields to web search schema
• Add custom reranker auth configuration in data-schemas
• Update loadWebSearchConfig to handle new fields

Motivation

Enable using any Jina-compatible /v1/rerank endpoint (Scaleway, vLLM, LiteLLM, etc.) as a reranker provider with fully configurable URL, API key, and model name. The docs already mention "Planned Rerankers: Additional third-party reranking services".

Configuration

webSearch:
  rerankerType: custom
  customRerankerApiUrl: "https://api.scaleway.ai/v1/rerank"
  customRerankerApiKey: "${SCALEWAY_API_KEY}"
  customRerankerModel: "qwen3-embedding-8b"

Test plan

• npm run build:data-provider succeeds
• No changes needed in packages/api/src/web/web.ts (generic auth loading handles new config automatically)
• No changes needed in handleTools.js (authResult spread passes fields through)

Depends on: danny-avila/agents#66
Relates to: #12119

Related issues:

• feat: Add COHERE_API_URL environment variable support for custom Cohere endpoints #9544 (feat: Add COHERE_API_URL environment variable support)
• [Enhancement]: Support Custom API endpoint for Cohere ReRanking #8710 (Support Custom API endpoint for Cohere ReRanking)
• [Bug]: rerankerType config does not permit all allowed types, and this option is not passed #10022 (rerankerType config does not permit all allowed types)
• 🔗 feat: Custom Jina API URL for Web Search Reranking #9236 (feat: Custom Jina API URL for Web Search Reranking)

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