Update `ToolCallingDemo` to support capability/provider resolution

[michalharakal]

Summary

Update demo code to use the new architecture.

Scope

• Add provider/capability-based resolution path
• Preserve explicit "llama3" and "chatml" options
• Add auto-detection path based on model metadata
• Show whether native or generic mode was selected

Acceptance criteria

• Demo can resolve provider automatically when metadata is sufficient
• Existing demo flows continue to work
• Explicit selection still works