feat: Add status bar item showing connection status

[josedab]

Description

Add a VS Code status bar item that shows whether the extension is connected to a Streamline server.

Task

• Create a status bar item (bottom bar) showing: 🟢 Connected / 🔴 Disconnected / 🟡 Connecting
• Update it when connection state changes
• Click should open the connection settings

Helpful Context

• See VS Code Status Bar API
• Look at existing extension activation in src/extension.ts