fix: Revert danger-full-access denylist-only mode

[viyatb-oai]

Summary

• Reverts [codex] Add danger-full-access denylist-only network mode #16946 and removes the danger-full-access denylist-only network mode.
• Removes the corresponding config requirements, app-server protocol/schema, config API, TUI debug output, and network proxy behavior.
• Drops stale tests that depended on the reverted mode while preserving newer managed allowlist-only coverage.

Verification

• just write-app-server-schema
• just fmt
• cargo test -p codex-config network_requirements
• cargo test -p codex-core network_proxy_spec
• cargo test -p codex-core managed_network_proxy_decider_survives_full_access_start
• cargo test -p codex-app-server map_requirements_toml_to_api
• cargo test -p codex-tui debug_config_output
• cargo test -p codex-app-server-protocol
• just fix -p codex-config -p codex-core -p codex-app-server-protocol -p codex-app-server -p codex-tui
• git diff --cached --check

Not run: full workspace cargo test (repo instructions ask for confirmation before that broader run).

[rreichel3-oai]

LGTM!