feat: vendor app-server protocol schema fixtures (#10371)

Similar to what @sayan-oai did in openai/codex#8956 for
`config.schema.json`, this PR updates the repo so that it includes the
output of `codex app-server generate-json-schema` and `codex app-server
generate-ts` and adds a test to verify it is in sync with the current
code.

Motivation:
- This makes any schema changes introduced by a PR transparent during
code review.
- In particular, this should help us catch PRs that would introduce a
non-backwards-compatible change to the app schema (eventually, this
should also be enforced by tooling).
- Once https://github.com/openai/codex/pull/10231 is in to formalize the
notion of "experimental" fields, we can work on ensuring the
non-experimental bits are backwards-compatible.

`codex-rs/app-server-protocol/tests/schema_fixtures.rs` was added as the
test and `just write-app-server-schema` can be use to generate the
vendored schema files.

Incidentally, when I run:

```
rg _ codex-rs/app-server-protocol/schema/typescript/v2
```

I see a number of `snake_case` names that should be `camelCase`.

justfile

@@ -68,6 +68,10 @@ mcp-server-run *args:
 write-config-schema:
     cargo run -p codex-core --bin codex-write-config-schema
 
+# Regenerate vendored app-server protocol schema artifacts.
+write-app-server-schema:
+    cargo run -p codex-app-server-protocol --bin write_schema_fixtures
+
 # Tail logs from the state SQLite database
 log *args:
     if [ "${1:-}" = "--" ]; then shift; fi; cargo run -p codex-state --bin logs_client -- "$@"