Feature Request: Add openOnStartup setting for VSCode extension

Feature Request

Add a claudeCode.openOnStartup setting to automatically open the Claude Code panel when VSCode starts.

Use Case

Many users want Claude Code to be immediately available when they open VSCode, without needing to manually open the panel each time. This is especially useful for developers who use Claude Code as their primary coding assistant.

Proposed Solution

Add a new boolean setting:

"claudeCode.openOnStartup": {
  "type": "boolean",
  "default": false,
  "description": "Automatically open the Claude Code panel when VSCode starts."
}

Current Workaround

Users can leave the panel open when closing VSCode, relying on VSCode's state restoration. However, this doesn't work reliably in all scenarios (e.g., when opening a new workspace).

Additional Context

This would align with how other assistant extensions (like GitHub Copilot Chat) handle startup behavior, improving the developer experience for users who rely heavily on Claude Code.