feat: implement mobile AI chat feature and fix duplicate response issue (#610)

Backend fixes:
- Fix duplicate AssistantResponseJob triggering causing duplicate AI responses
- UserMessage model already handles job triggering via after_create_commit callback
- Remove redundant job enqueue in chats_controller and messages_controller

Mobile app features:
- Implement complete AI chat interface and conversation management
- Add Chat, Message, and ToolCall data models
- Add ChatProvider for state management with polling mechanism
- Add ChatService to handle all chat-related API requests
- Add chat list screen (ChatListScreen)
- Add conversation detail screen (ChatConversationScreen)
- Refactor navigation structure with bottom navigation bar (MainNavigationScreen)
- Add settings screen (SettingsScreen)
- Optimize TransactionsProvider to support account filtering

Technical details:
- Implement message polling mechanism for real-time AI responses
- Support chat creation, deletion, retry and other operations
- Integrate Material Design 3 design language
- Improve user experience and error handling

Co-authored-by: dwvwdv <dwvwdv@protonmail.com>

app/controllers/api/v1/chats_controller.rb

@@ -28,7 +28,12 @@ class Api::V1::ChatsController < Api::V1::BaseController
         )
 
         if @message.save
-          AssistantResponseJob.perform_later(@message)
+          # NOTE: Commenting out duplicate job enqueue to fix mobile app receiving duplicate AI responses
+          # UserMessage model already triggers AssistantResponseJob via after_create_commit callback
+          # in app/models/user_message.rb:10-12, so this manual enqueue causes the job to run twice,
+          # resulting in duplicate AI responses with different content and wasted tokens.
+          # See: https://github.com/dwvwdv/sure (mobile app integration issue)
+          # AssistantResponseJob.perform_later(@message)
           render :show, status: :created
         else
           @chat.destroy

app/controllers/api/v1/messages_controller.rb

@@ -13,7 +13,12 @@ class Api::V1::MessagesController < Api::V1::BaseController
     )
 
     if @message.save
-      AssistantResponseJob.perform_later(@message)
+      # NOTE: Commenting out duplicate job enqueue to fix mobile app receiving duplicate AI responses
+      # UserMessage model already triggers AssistantResponseJob via after_create_commit callback
+      # in app/models/user_message.rb:10-12, so this manual enqueue causes the job to run twice,
+      # resulting in duplicate AI responses with different content and wasted tokens.
+      # See: https://github.com/dwvwdv/sure (mobile app integration issue)
+      # AssistantResponseJob.perform_later(@message)
       render :show, status: :created
     else
       render json: { error: "Failed to create message", details: @message.errors.full_messages }, status: :unprocessable_entity