refactor(network-proxy): flatten network config under [network]

[viyatb-oai]

Summary:

• Rename config table from network_proxy to network.
• Flatten allowed_domains, denied_domains, allow_unix_sockets, and allow_local_binding onto NetworkProxySettings.
• Update runtime, state constraints, tests, and README to the new config shape.

[chatgpt-codex-connector]

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