fix: honor proxy env vars in web search HTTP calls

[serhiizghama]

Problem

The web search pipeline's HTTP calls (Tavily search/extract, Serper search/scrape, SearXNG, Firecrawl, Jina and Cohere rerankers) go through axios without any proxy handling. In corporate/enterprise deployments where outbound traffic must pass through a forward proxy, these calls bypass the proxy and fail with 502:

error: Error in search: Tavily API request failed: Request failed with status code 502

Reported in danny-avila/LibreChat#13483. Notably, axios' built-in env-var proxy support doesn't help here because it does not establish a CONNECT tunnel for HTTPS targets — the standard workaround is HttpsProxyAgent with axios' own proxy handling disabled (proxy: false), which the reporter verified works in their environment.

Solution

• New getAxiosProxyOptions(url) helper in src/tools/search/proxy.ts:
  • honors the PROXY variable first — same convention as the existing HttpsProxyAgent usage in ToolSearch, CodeExecutor, and BashExecutor
  • falls back to the standard HTTPS_PROXY/HTTP_PROXY/NO_PROXY variables via proxy-from-env, so self-hosted endpoints (SearXNG, Firecrawl) can be excluded with NO_PROXY exactly like MCP connections already allow
  • only applies to https: URLs — plain-HTTP targets keep axios' default behavior, which handles HTTP proxying correctly
• Spread the resolved options into all eight axios call sites in src/tools/search/
• https-proxy-agent was already a dependency; proxy-from-env is added (it's tiny and already in the tree as an axios dependency)

Testing

• npx jest src/tools/search/ — 56 tests pass, including new coverage for: no-proxy default, PROXY precedence over HTTPS_PROXY, empty-string handling, NO_PROXY exclusions, and non-HTTPS passthrough
• npx tsc --noEmit and npx eslint clean, npm run build succeeds

Closes danny-avila/LibreChat#13483 (the affected code lives here).