chore(app-server): add experimental annotation to relevant fields (#10928)

These fields had always been documented as experimental/unstable with
docstrings, but now let's actually use the `experimental` annotation to
be more explicit.

- thread/start.experimentalRawEvents
- thread/resume.history
- thread/resume.path
- thread/fork.path
- turn/start.collaborationMode
- account/login/start.chatgptAuthTokens

codex-rs/app-server-protocol/schema/json/v2/ThreadForkParams.json

@@ -69,13 +69,6 @@
         "null"
       ]
     },
-    "path": {
-      "description": "[UNSTABLE] Specify the rollout path to fork from. If specified, the thread_id param will be ignored.",
-      "type": [
-        "string",
-        "null"
-      ]
-    },
     "sandbox": {
       "anyOf": [
         {