Feat: Preserve network access on read-only sandbox policies

[celia-oai]

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.