- Implemented Gateway HTTP request handler with method routing
* Added handle(), handle_get(), handle_head(), handle_post(), handle_options()
* Integrated GatewayRequest and HttpResponse types
* Added create_upload_response() for upload functionality
- Integrated ContentRouter into StorageNetwork
* Added router field to StorageNetwork struct
* Added router() and router_mut() accessor methods
- Fixed dead code warnings for gateway handler components
This completes the gateway HTTP handling infrastructure and content routing.
Previously these types were defined but unused, causing dead code warnings.
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