fix: Revert danger-full-access denylist-only mode (#17732)

## Summary

- Reverts openai/codex#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).

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -899,7 +899,6 @@ pub struct NetworkRequirements {
     /// Legacy compatibility view derived from `unix_sockets`.
     pub allow_unix_sockets: Option<Vec<String>>,
     pub allow_local_binding: Option<bool>,
-    pub danger_full_access_denylist_only: Option<bool>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq, JsonSchema, TS)]
@@ -8103,7 +8102,6 @@ mod tests {
                 dangerously_allow_all_unix_sockets: None,
                 domains: None,
                 managed_allowed_domains_only: None,
-                danger_full_access_denylist_only: None,
                 allowed_domains: Some(vec!["api.openai.com".to_string()]),
                 denied_domains: Some(vec!["blocked.example.com".to_string()]),
                 unix_sockets: None,
@@ -8130,7 +8128,6 @@ mod tests {
                 ),
             ])),
             managed_allowed_domains_only: Some(true),
-            danger_full_access_denylist_only: Some(true),
             allowed_domains: Some(vec!["api.openai.com".to_string()]),
             denied_domains: Some(vec!["blocked.example.com".to_string()]),
             unix_sockets: Some(BTreeMap::from([
@@ -8161,7 +8158,6 @@ mod tests {
                     "blocked.example.com": "deny"
                 },
                 "managedAllowedDomainsOnly": true,
-                "dangerFullAccessDenylistOnly": true,
                 "allowedDomains": ["api.openai.com"],
                 "deniedDomains": ["blocked.example.com"],
                 "unixSockets": {