feat: support companyAnnouncements / customizable welcome text in VS Code extension UI

Feature Request

Summary

The companyAnnouncements setting in ~/.claude/settings.json currently only works in the CLI (terminal) output. It has no effect on the VS Code extension's welcome screen UI.

Current Behavior

• In the VS Code extension, the welcome screen displays a randomly rotating hardcoded tagline (e.g. "Ready to code? Let's write something worth deploying.").
• The companyAnnouncements array in settings.json is ignored by the VS Code extension UI — announcements only appear in the terminal/CLI.

Desired Behavior

Allow companyAnnouncements (or a similar setting) to surface in the VS Code extension UI, for example:

• Replace or augment the rotating tagline on the welcome screen
• Display a banner/notice below the chat input field
• Or any other visible location in the extension panel

Use Case

Enterprise / team deployments often need to display custom notices to users — such as:

• Identifying the environment (e.g. "Powered by Azure AI Foundry – Internal Use Only")
• Compliance or usage reminders
• Onboarding instructions

Currently this is only possible in the CLI context, leaving VS Code extension users without this information.

Settings Example

// ~/.claude/settings.json
{
  "companyAnnouncements": [
    "Welcome to Claude Code – Supported by MS Foundry – COMPANY Subscription!",
    "Reminder: This is an internal environment. Do not share access outside the designated team."
  ]
}

Environment

• Claude Code VS Code Extension
• ~/.claude/settings.json (user-level settings)