Parent Issue

Closes #406

Summary

Implement the http2_server_stream class for handling server-side stream responses.

Tasks

• Create include/kcenon/network/protocols/http2/http2_server_stream.h
• Implement response methods (send_headers, send_data)
• Implement streaming response support (start_response, write, end_response)
• Implement stream control (reset)
• Add request info accessors (stream_id, method, path, headers)

Files to Create

• include/kcenon/network/protocols/http2/http2_server_stream.h

Acceptance Criteria

• Can send headers with status code
• Can send data frames
• Streaming response works correctly
• Stream state management correct