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/v1/AuthStatusChangeNotification.json

@@ -0,0 +1,46 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "definitions": {
+    "AuthMode": {
+      "description": "Authentication mode for OpenAI-backed providers.",
+      "oneOf": [
+        {
+          "description": "OpenAI API key provided by the caller and stored by Codex.",
+          "enum": [
+            "apikey"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "ChatGPT OAuth managed by Codex (tokens persisted and refreshed by Codex).",
+          "enum": [
+            "chatgpt"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "[UNSTABLE] FOR OPENAI INTERNAL USE ONLY - DO NOT USE.\n\nChatGPT auth tokens are supplied by an external host app and are only stored in memory. Token refresh must be handled by the external host app.",
+          "enum": [
+            "chatgptAuthTokens"
+          ],
+          "type": "string"
+        }
+      ]
+    }
+  },
+  "description": "Deprecated notification. Use AccountUpdatedNotification instead.",
+  "properties": {
+    "authMethod": {
+      "anyOf": [
+        {
+          "$ref": "#/definitions/AuthMode"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    }
+  },
+  "title": "AuthStatusChangeNotification",
+  "type": "object"
+}