feat: add initial Hold Slayer AI telephony gateway implementation

Complete project scaffolding and core implementation of an AI-powered
telephony system that calls companies, navigates IVR menus, waits on
hold, and transfers to the user when a human answers.

Key components:
- FastAPI server with REST API, WebSocket, and MCP (SSE) interfaces
- SIP/VoIP call management via PJSUA2 with RTP audio streaming
- LLM-powered IVR navigation using OpenAI/Anthropic with tool calling
- Hold detection service combining audio analysis and silence detection
- Real-time STT (Whisper/Deepgram) and TTS (OpenAI/Piper) pipelines
- Call recording with per-channel and mixed audio capture
- Event bus (asyncio pub/sub) for real-time client updates
- Web dashboard with live call monitoring
- SQLite persistence via SQLAlchemy with call history and analytics
- Notification support (email, SMS, webhook, desktop)
- Docker Compose deployment with Opal VoIP and Opal Media containers
- Comprehensive test suite with unit, integration, and E2E tests
- Simplified .gitignore and full project documentation in README

docs/README.md

@@ -0,0 +1,18 @@
+# Hold Slayer Documentation
+
+Comprehensive documentation for the Hold Slayer AI telephony gateway.
+
+## Contents
+
+| Document | Description |
+|----------|-------------|
+| [Architecture](architecture.md) | System architecture, component diagram, data flow |
+| [Core Engine](core-engine.md) | SIP engine, media pipeline, call manager, event bus |
+| [Hold Slayer Service](hold-slayer-service.md) | IVR navigation, hold detection, human detection, transfer |
+| [Audio Classifier](audio-classifier.md) | Waveform analysis, feature extraction, classification logic |
+| [Services](services.md) | LLM client, transcription, recording, analytics, notifications |
+| [Call Flows](call-flows.md) | Call flow model, step types, learner, CRUD API |
+| [API Reference](api-reference.md) | REST endpoints, WebSocket protocol, request/response schemas |
+| [MCP Server](mcp-server.md) | MCP tools and resources for AI assistant integration |
+| [Configuration](configuration.md) | Environment variables, settings, deployment options |
+| [Development](development.md) | Setup, testing, contributing, project conventions |