Refactor API routes and controllers for improved structure and clarity

- Updated API route structure to remove versioning and consolidate endpoints.
- Refactored routing in `server.go` to use a unified `/api` prefix for all controllers.
- Added new `ChannelController`, `ConversationController`, and `MessageController` to handle specific API functionalities.
- Removed deprecated `OpenImContextMiddleware` and related logic.
- Enhanced channel validation logic in `ChannelService` and `ChannelRepository`.
- Updated frontend API calls to align with new endpoint structure.

web/lib/sdk/cs-ai-agent-sdk.js

@@ -100,7 +100,7 @@
     if (!baseUrl || !config.channelId || typeof fetch !== "function") {
       return Promise.resolve(config);
     }
-    var url = baseUrl + "/api/open/im/widget/config?channelId=" + encodeURIComponent(config.channelId);
+    var url = baseUrl + "/api/channel/config?channelId=" + encodeURIComponent(config.channelId);
     return fetch(url, {
       method: "GET",
       cache: "no-store",