Implement LLM bridge endpoint for fcctl-core

[AlexMikhalev]

Summary

Implement LLM bridge endpoint for querying LLMs from within VMs.

Context

PR #426 (feat(rlm): RLM orchestration with MCP tools) requires LLM bridge functionality to allow VMs to query LLMs.

Requirements

The implementation should provide:

1. HTTP endpoint for LLM queries
2. Authentication and authorization
3. Request/response handling
4. Integration with existing LLM services

Related

Blocked by: #664 (Create fcctl-core crate)