permissions: remove macOS seatbelt extension profiles (#15918)

## Why

`PermissionProfile` should only describe the per-command permissions we
still want to grant dynamically. Keeping
`MacOsSeatbeltProfileExtensions` in that surface forced extra macOS-only
approval, protocol, schema, and TUI branches for a capability we no
longer want to expose.

## What changed

- Removed the macOS-specific permission-profile types from
`codex-protocol`, the app-server v2 API, and the generated
schema/TypeScript artifacts.
- Deleted the core and sandboxing plumbing that threaded
`MacOsSeatbeltProfileExtensions` through execution requests and seatbelt
construction.
- Simplified macOS seatbelt generation so it always includes the fixed
read-only preferences allowlist instead of carrying a configurable
profile extension.
- Removed the macOS additional-permissions UI/docs/test coverage and
deleted the obsolete macOS permission modules.
- Tightened `request_permissions` intersection handling so explicitly
empty requested read lists are preserved only when that field was
actually granted, avoiding zero-grant responses being stored as active
permissions.

codex-rs/app-server/src/transport/mod.rs

@@ -801,7 +801,6 @@ mod tests {
                                         write: None,
                                     },
                                 ),
-                                macos: None,
                             },
                         ),
                         proposed_execpolicy_amendment: None,
@@ -864,7 +863,6 @@ mod tests {
                                         write: None,
                                     },
                                 ),
-                                macos: None,
                             },
                         ),
                         proposed_execpolicy_amendment: None,
@@ -891,7 +889,6 @@ mod tests {
                     "read": [allowed_path],
                 "write": null,
                 },
-                "macos": null,
             })
         );
     }