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`.

codex-rs/app-server-protocol/src/bin/write_schema_fixtures.rs

@@ -0,0 +1,32 @@
+use anyhow::Context;
+use anyhow::Result;
+use clap::Parser;
+use std::path::PathBuf;
+
+#[derive(Parser, Debug)]
+#[command(about = "Regenerate vendored app-server schema fixtures")]
+struct Args {
+    /// Root directory containing `typescript/` and `json/`.
+    #[arg(long = "schema-root", value_name = "DIR")]
+    schema_root: Option<PathBuf>,
+
+    /// Optional path to the Prettier executable to format generated TypeScript files.
+    #[arg(short = 'p', long = "prettier", value_name = "PRETTIER_BIN")]
+    prettier: Option<PathBuf>,
+}
+
+fn main() -> Result<()> {
+    let args = Args::parse();
+
+    let schema_root = args
+        .schema_root
+        .unwrap_or_else(|| PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("schema"));
+
+    codex_app_server_protocol::write_schema_fixtures(&schema_root, args.prettier.as_deref())
+        .with_context(|| {
+            format!(
+                "failed to regenerate schema fixtures under {}",
+                schema_root.display()
+            )
+        })
+}