Add comprehensive "Understanding SIP for Home Assistant" tutorial with voice assistant integration

[Copilot]

This PR addresses the documentation gap identified in issue #37 by adding a comprehensive tutorial page that explains SIP fundamentals before users dive into setup instructions.

What's Added

The new /docs/tutorial/what-is-sip.md page provides:

• Clear SIP Definition: Explains Session Initiation Protocol as a communication protocol for real-time sessions (voice, video, messaging)
• Comprehensive Use Cases: Details four key applications:
  • 🔔 Doorbell Integration: SIP doorbells, call reception, dashboard interaction
  • 📞 Internal Communication: Home phone systems, intercom functionality
  • 🏠 Smart Home Automation: Call-triggered automations, device integration
  • 🎤 Voice Assistant Integration: Voice-activated dialing, hands-free communication through smart speakers
• Essential Concepts: Covers PBX, WebRTC, WebSocket (WS/WSS), and SIP endpoints with beginner-friendly explanations
• Accurate Architecture Overview: Includes a Mermaid diagram showing the correct SIP-HASS component flow:

  SIP Devices → Asterisk PBX → Ingress Add-on → SIP Integration → SIP Cards → Dashboard/Mobile App
  

• Real-World Example: Step-by-step walkthrough of a doorbell call scenario

Key Improvements

• Voice Assistant Support: Added comprehensive coverage of Home Assistant voice assistant integration, including voice-activated dialing and hands-free communication workflows
• Corrected Architecture: Updated diagram and explanations to accurately reflect how SIP Integration connects to SIP Cards rather than directly to dashboard components
• Enhanced Technical Concepts: Added WebSocket (WS/WSS) explanations for real-time communication features
• Better Title: Changed from "What is SIP?" to "Understanding SIP for Home Assistant" for clearer context

Page Positioning

The page is strategically placed at sidebar_position: 2 in the tutorial flow, appearing after the introduction but before technical setup. This ensures users understand the underlying technology before following installation guides.

The page features proper navigation, automatic table of contents generation, and a visual diagram that helps users understand the complete SIP-HASS ecosystem at a glance.

Fixes #37.

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[TECH7Fox]

@copilot please also include calling with home assistant's voice assistants as one of the features / use cases. Also give it another title. The diagram is missing ingress and integration, and SIP core connects to the different cards, not dashboard and app. And add WS / WSS to key concepts.

Screenshot is great though, please give another one with these changes :)

[Copilot]

@copilot please also include calling with home assistant's voice assistants as one of the features / use cases. Also give it another title. The diagram is missing ingress and integration, and SIP core...

I've updated the tutorial page with all the requested changes:

✅ New title: Changed to "Understanding SIP for Home Assistant"
✅ Voice assistant integration: Added as a fourth use case with voice-activated dialing and hands-free communication
✅ Fixed diagram: Updated Mermaid diagram to show proper architecture with Ingress Add-on and SIP Integration, with SIP Core connecting to cards instead of dashboard directly
✅ Added WS/WSS: Included WebSocket concepts in the Key Concepts section explaining real-time communication

The page now accurately reflects the SIP-HASS architecture and includes comprehensive coverage of voice assistant integration capabilities.

Commit: fb21176