Ktor extensions for StreamableHttpServerTransport

[kpavlov]

Create Ktor extensions for StreamableHttpServerTransport.

Server should support both stateful and stateless operation mode.

1. Application-level extensions.

API might look like. Naming is an open question

application {
   routing {
     mcpStreamableHttp(config: StreamableHttpServerTransport.Configuration) { mcpServer }
   }
}

2. Route-level extensions. API might look like

application {
    install(SSE)
    routing {
        route("/mcp") {
            mcpStreamableHttp(config: StreamableHttpServerTransport.Configuration) { mcpServer }
        }
    }
}

Definition of Done:

For both (Application+Route level extensions) x (Statefull+stateless mode) = (4 combinations):

1. Routes implemented
2. Integration test for happy scenario
3. Unit tests for route initialization, like this

Related PRs:

• Ktor extensions for streamable http #504 initial implementation
• feat: introduce StreamableHttpServerTransport.Configuration #560 streamable transport configuration
• refactor: replace flat parameter definitions with StreamableHttpServerTransport.Configuration in Application Ktor extensions #563
• feat: Verify MCP endpoints with authentication for Streamable HTTP transport, test for SSE transport #535

[kpavlov]

The initial implementation (#504) exposes all configuration options as method parameters, making the API surface fragile to future additions of parameters. That is why #560 and eventually another PR are needed.