Avoid JSON-schema canonicalization (preserve field order)

Motivation:
- App-server JSON schema output is already stable; sorting object keys is unnecessary.
- Alphabetical key canonicalization is potentially harmful because it obscures intentional ordering (e.g. struct field order) and makes diffs noisier.

What changed:
- Remove JSON key-sorting from schema emission.
- Regenerate vendored JSON schema fixtures.

Refs: openai/codex#8956 (fixture sync test pattern)

codex-rs/app-server-protocol/schema/json/JSONRPCNotification.json

@@ -0,0 +1,15 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "description": "A notification which does not expect a response.",
+  "properties": {
+    "method": {
+      "type": "string"
+    },
+    "params": true
+  },
+  "required": [
+    "method"
+  ],
+  "title": "JSONRPCNotification",
+  "type": "object"
+}