Upgrade a React app from CometChat UI Kit v6 → v7 (`@cometchat/chat-uikit-react` ^6 → ^7). Reads the repo's CometChat usage, applies the breaking-change map (deps, symbol renames, RxJS events → `useCometChatEvents`, DataSource → plugins, templates → plugins, theme prop, calling), fetches the prop-by-prop guide, and verifies the build. Triggers: 'upgrade my v6 uikit to v7', 'migrate cometchat react v6 to v7', 'upgrade @cometchat/chat-uikit-react to v7', 'cometchat v6 to v7', 'bump cometchat uikit'.
