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/TurnStartParams.json

@@ -383,17 +383,6 @@
       ],
       "description": "Override the approval policy for this turn and subsequent turns."
     },
-    "collaborationMode": {
-      "anyOf": [
-        {
-          "$ref": "#/definitions/CollaborationMode"
-        },
-        {
-          "type": "null"
-        }
-      ],
-      "description": "EXPERIMENTAL - set a pre-set collaboration mode. Takes precedence over model, reasoning_effort, and developer instructions if set."
-    },
     "cwd": {
       "description": "Override the working directory for this turn and subsequent turns.",
       "type": [