feat(intellij): support chat panel

[wwayne]

Screen record: https://jam.dev/c/0b01b2cc-aa25-4a3f-b3c7-980d184be3eb

Completed:

• Chat panel positioned on the right
• Ability to display loading and unauthorized warning messages
• Theme color and font size synchronized with the IntelliJ editor

Still Missing:

• Support for commands (e.g., "explain this")
• VSCode 1.8 features (e.g., send selected code with the message)

Needs Improvement:

(Already marked as FIXME in the code)

• Listen for the editor's theme change events to update the chat panel's theme accordingly
• Refactor the thread implementation to handle sending and receiving messages from the /chat page
• Detect web server health to ensure the instance is up and confirm the chat model's availability

Tip

Right-click to open the dev tool (chrome liked dev tool)