Add REST GET /config endpoint to fetch agent configuration

[Copilot]

Adds /config endpoint to expose the agent's runtime configuration as JSON.

Changes

• RestService routing: Added createConfigRoutings() method that serializes ConfigOptions map to JSON using nlohmann::json
• Variant handling: Visitor pattern handles all ConfigOption types (bool, int, string, double, Seconds, Milliseconds, StringList) with compile-time exhaustiveness check
• Test coverage: Added test verifying response format, status code, and presence of key configuration values

Usage

curl http://localhost:5000/config

Returns:

{
  "Port": 5000,
  "BufferSize": 17,
  "SchemaVersion": "2.6",
  "MaxAssets": 4,
  ...
}

String values are properly escaped via nlohmann::json to prevent injection attacks.

Original prompt

add a rest GET to fetch the agent config

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