fix(provider): allow remote local-network hosts when proxy env vars are set

[jeevan6996]

Summary

• detect local-network and LAN-style baseURL hosts (private IP ranges, .local, single-label hostnames)
• automatically add those hosts to NO_PROXY/no_proxy when HTTP(S)_PROXY is configured so requests bypass corporate proxies
• keep public hosts proxied; add tests for private-host and public-host behavior

Testing

• bun test test/provider/provider.test.ts --test-name-pattern ensureNoProxyForBaseURL
• bun test test/provider/provider.test.ts --test-name-pattern plugin\ config\ providers\ persist\ after\ instance\ dispose|plugin\ config\ enabled\ and\ disabled\ providers\ are\ honored

Closes #23900

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