Support forced workspace ids in requirements

Allow requirements.toml and cloud requirements to specify forced_chatgpt_workspace_id using the same single string or array shape as config.toml.

Prefer the requirements value during config resolution, expose it through configRequirements/read, and regenerate app-server schema fixtures.

Document requirements precedence and add targeted coverage for requirements parsing, config resolution, API mapping, and cloud requirements fixtures.

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -3539,6 +3539,16 @@
             "object",
             "null"
           ]
+        },
+        "forcedChatgptWorkspaceId": {
+          "anyOf": [
+            {
+              "$ref": "#/definitions/ForcedChatgptWorkspaceIds"
+            },
+            {
+              "type": "null"
+            }
+          ]
         }
       },
       "type": "object"