feat: send session/request ID to LLM provider for call grouping

[a6b8]

Problem

When reviewing LLM provider activity (e.g. OpenRouter dashboard), the "App" column shows "Unknown" for all calls from mcp-agent-server. This makes it impossible to:

• Group calls that belong to the same user request
• Distinguish which agent made which call
• Analyze cost per conversation/session

Proposal

The mcp-agent-server should send identifying metadata with each LLM call so providers can display it in their dashboards:

1. App Name

Send a static app identifier (e.g. X-Title header for OpenRouter) so calls show up as "Anschluss Mobility" instead of "Unknown".

2. Session/Request ID

Send a unique session or request ID with each call so all sub-agent calls from one user question can be grouped together. For example:

• User asks: "How do I get from the station to my office?"
• Main Agent call → session: req-abc123
• Bahnhof Agent call → session: req-abc123
• Weather Agent call → session: req-abc123
• Navigator Agent call → session: req-abc123

All 4 calls would be grouped under req-abc123 in the provider dashboard.

3. Agent Name

Include the agent name (e.g. ticketkauf, radparken) so you can see which specialist made the call.

Implementation Ideas

OpenRouter supports these headers:

• X-Title — App name shown in dashboard
• HTTP-Referer — Can be used for grouping

A possible approach:

• Generate a sessionId per incoming user request in the server
• Pass it through to all sub-agent LLM calls
• Set X-Title to {appName}/{agentName}

Context

Discovered during cost analysis of the "Anschluss erreichen" Hackathon (March 2026). 251 calls, $4.22 total — but impossible to tell which calls belonged to which user question.