Feat: Preserve network access on read-only sandbox policies (#13409)

## Summary

`PermissionProfile.network` could not be preserved when additional or
compiled permissions resolved to
`SandboxPolicy::ReadOnly`, because `ReadOnly` had no network_access
field. This change makes read-only + network
enabled representable directly and threads that through the protocol,
app-server v2 mirror, and permission-
  merging logic.

## What changed

- Added `network_access: bool` to `SandboxPolicy::ReadOnly` in the core
protocol and app-server v2 protocol.
- Kept backward compatibility by defaulting the new field to false, so
legacy read-only payloads still
    deserialize unchanged.
- Updated `has_full_network_access()` and sandbox summaries to respect
read-only network access.
  - Preserved PermissionProfile.network when:
      - compiling skill permission profiles into sandbox policies
      - normalizing additional permissions
      - merging additional permissions into existing sandbox policies
- Updated the approval overlay to show network in the rendered
permission rule when requested.
  - Regenerated app-server schema fixtures for the new v2 wire shape.

codex-rs/utils/sandbox-summary/src/sandbox_summary.rs

@@ -4,7 +4,13 @@ use codex_protocol::protocol::SandboxPolicy;
 pub fn summarize_sandbox_policy(sandbox_policy: &SandboxPolicy) -> String {
     match sandbox_policy {
         SandboxPolicy::DangerFullAccess => "danger-full-access".to_string(),
-        SandboxPolicy::ReadOnly { .. } => "read-only".to_string(),
+        SandboxPolicy::ReadOnly { network_access, .. } => {
+            let mut summary = "read-only".to_string();
+            if *network_access {
+                summary.push_str(" (network access enabled)");
+            }
+            summary
+        }
         SandboxPolicy::ExternalSandbox { network_access } => {
             let mut summary = "external-sandbox".to_string();
             if matches!(network_access, NetworkAccess::Enabled) {
@@ -66,6 +72,15 @@ mod tests {
         assert_eq!(summary, "external-sandbox (network access enabled)");
     }
 
+    #[test]
+    fn summarizes_read_only_with_enabled_network() {
+        let summary = summarize_sandbox_policy(&SandboxPolicy::ReadOnly {
+            access: Default::default(),
+            network_access: true,
+        });
+        assert_eq!(summary, "read-only (network access enabled)");
+    }
+
     #[test]
     fn workspace_write_summary_still_includes_network_access() {
         let root = if cfg!(windows) { "C:\\repo" } else { "/repo" };