Contextual chat in IntelliJ IDEA

Extend the IntelliJ IDEA plugin to support contextual chats as Gemini Code Assist. Basic workflow would be like:

1. Focus an editor window and possibly select text in the editor
2. Open contextual chat from the contextual menu or with a key command
3. Interact contextually with Claude Code

<img width="1189" alt="Image" src="https://github.com/user-attachments/assets/a57ce748-3e91-4dd6-8808-3c1cbb7c7fd0" />