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/schema/json/v2/LoginAccountParams.json

@@ -0,0 +1,69 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "oneOf": [
+    {
+      "properties": {
+        "apiKey": {
+          "type": "string"
+        },
+        "type": {
+          "enum": [
+            "apiKey"
+          ],
+          "title": "ApiKeyv2::LoginAccountParamsType",
+          "type": "string"
+        }
+      },
+      "required": [
+        "apiKey",
+        "type"
+      ],
+      "title": "ApiKeyv2::LoginAccountParams",
+      "type": "object"
+    },
+    {
+      "properties": {
+        "type": {
+          "enum": [
+            "chatgpt"
+          ],
+          "title": "Chatgptv2::LoginAccountParamsType",
+          "type": "string"
+        }
+      },
+      "required": [
+        "type"
+      ],
+      "title": "Chatgptv2::LoginAccountParams",
+      "type": "object"
+    },
+    {
+      "description": "[UNSTABLE] FOR OPENAI INTERNAL USE ONLY - DO NOT USE. The access token must contain the same scopes that Codex-managed ChatGPT auth tokens have.",
+      "properties": {
+        "accessToken": {
+          "description": "Access token (JWT) supplied by the client. This token is used for backend API requests.",
+          "type": "string"
+        },
+        "idToken": {
+          "description": "ID token (JWT) supplied by the client.\n\nThis token is used for identity and account metadata (email, plan type, workspace id).",
+          "type": "string"
+        },
+        "type": {
+          "enum": [
+            "chatgptAuthTokens"
+          ],
+          "title": "ChatgptAuthTokensv2::LoginAccountParamsType",
+          "type": "string"
+        }
+      },
+      "required": [
+        "accessToken",
+        "idToken",
+        "type"
+      ],
+      "title": "ChatgptAuthTokensv2::LoginAccountParams",
+      "type": "object"
+    }
+  ],
+  "title": "LoginAccountParams"
+}