feat(menu): Add Settings menu item

[CalvinAllen]

Description

Add a "Settings..." menu item to the Tools > VSMCP menu that opens the extension's options page.

Implementation

• Add new button in VSCommandTable.vsct under VSMCPSettingsGroup
• Add command handler in ServerCommands.cs
• Use VS.Settings.OpenAsync() or equivalent to open the options page

Menu Structure (from plan)

Tools > VSMCP
├── Start Server
├── Stop Server
├── Restart Server
├── ─────────────
├── Copy Server URL
├── ─────────────
└── Settings...  <-- This one