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

db/__init__.py

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+"""Database layer — PostgreSQL connection, ORM models, and migrations."""

db/database.py

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+"""
+Database connection and session management.
+
+PostgreSQL via asyncpg + SQLAlchemy async.
+"""
+
+from datetime import datetime
+
+from sqlalchemy import (
+    JSON,
+    Column,
+    DateTime,
+    Float,
+    Integer,
+    String,
+    Text,
+    func,
+)
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.orm import DeclarativeBase
+
+from config import get_settings
+
+
+class Base(DeclarativeBase):
+    """SQLAlchemy declarative base for all ORM models."""
+
+    pass
+
+
+# ============================================================
+# ORM Models
+# ============================================================
+
+
+class CallRecord(Base):
+    __tablename__ = "call_records"
+
+    id = Column(String, primary_key=True)
+    direction = Column(String, nullable=False)  # inbound / outbound
+    remote_number = Column(String, index=True, nullable=False)
+    status = Column(String, nullable=False)  # completed / missed / failed / active / on_hold
+    mode = Column(String, nullable=False)  # direct / hold_slayer / ai_assisted
+    intent = Column(Text)  # What the user wanted (for hold_slayer)
+    started_at = Column(DateTime, default=func.now())
+    ended_at = Column(DateTime, nullable=True)
+    duration = Column(Integer, default=0)  # seconds
+    hold_time = Column(Integer, default=0)  # seconds spent on hold
+    device_used = Column(String)
+    recording_path = Column(String, nullable=True)
+    transcript = Column(Text, nullable=True)
+    summary = Column(Text, nullable=True)
+    action_items = Column(JSON, nullable=True)
+    sentiment = Column(String, nullable=True)
+    call_flow_id = Column(String, nullable=True)  # which flow was used
+    classification_timeline = Column(JSON, nullable=True)  # [{time, type, confidence}, ...]
+    metadata_ = Column("metadata", JSON, nullable=True)
+
+    def __repr__(self) -> str:
+        return f"<CallRecord {self.id} {self.remote_number} {self.status}>"
+
+
+class StoredCallFlow(Base):
+    __tablename__ = "call_flows"
+
+    id = Column(String, primary_key=True)
+    name = Column(String, nullable=False)
+    phone_number = Column(String, index=True, nullable=False)
+    description = Column(Text)
+    steps = Column(JSON, nullable=False)  # Serialized list[CallFlowStep]
+    last_verified = Column(DateTime, nullable=True)
+    avg_hold_time = Column(Integer, nullable=True)
+    success_rate = Column(Float, nullable=True)
+    times_used = Column(Integer, default=0)
+    last_used = Column(DateTime, nullable=True)
+    notes = Column(Text, nullable=True)
+    tags = Column(JSON, default=list)
+    created_at = Column(DateTime, default=func.now())
+    updated_at = Column(DateTime, default=func.now(), onupdate=func.now())
+
+    def __repr__(self) -> str:
+        return f"<StoredCallFlow {self.id} {self.phone_number}>"
+
+
+class Contact(Base):
+    __tablename__ = "contacts"
+
+    id = Column(String, primary_key=True)
+    name = Column(String, nullable=False)
+    phone_numbers = Column(JSON, nullable=False)  # [{number, label, primary}, ...]
+    category = Column(String)  # personal / business / service
+    routing_preference = Column(String, nullable=True)  # how to handle their calls
+    notes = Column(Text, nullable=True)
+    call_count = Column(Integer, default=0)
+    last_call = Column(DateTime, nullable=True)
+    created_at = Column(DateTime, default=func.now())
+    updated_at = Column(DateTime, default=func.now(), onupdate=func.now())
+
+    def __repr__(self) -> str:
+        return f"<Contact {self.id} {self.name}>"
+
+
+class Device(Base):
+    __tablename__ = "devices"
+
+    id = Column(String, primary_key=True)
+    name = Column(String, nullable=False)  # "Office SIP Phone"
+    type = Column(String, nullable=False)  # sip_phone / cell / tablet / softphone
+    sip_uri = Column(String, nullable=True)  # sip:robert@gateway.helu.ca
+    phone_number = Column(String, nullable=True)  # For PSTN devices
+    priority = Column(Integer, default=10)  # Routing priority (lower = higher priority)
+    is_online = Column(String, default="false")
+    capabilities = Column(JSON, default=list)  # ["voice", "video", "sms"]
+    last_seen = Column(DateTime, nullable=True)
+    created_at = Column(DateTime, default=func.now())
+    updated_at = Column(DateTime, default=func.now(), onupdate=func.now())
+
+    def __repr__(self) -> str:
+        return f"<Device {self.id} {self.name} ({self.type})>"
+
+
+# ============================================================
+# Engine & Session
+# ============================================================
+
+_engine = None
+_session_factory = None
+
+
+def get_engine():
+    """Get or create the async engine."""
+    global _engine
+    if _engine is None:
+        settings = get_settings()
+        _engine = create_async_engine(
+            settings.database_url,
+            echo=settings.debug,
+            pool_size=10,
+            max_overflow=20,
+        )
+    return _engine
+
+
+def get_session_factory() -> async_sessionmaker[AsyncSession]:
+    """Get or create the session factory."""
+    global _session_factory
+    if _session_factory is None:
+        _session_factory = async_sessionmaker(
+            get_engine(),
+            class_=AsyncSession,
+            expire_on_commit=False,
+        )
+    return _session_factory
+
+
+async def get_db() -> AsyncSession:
+    """Dependency: yield an async database session."""
+    factory = get_session_factory()
+    async with factory() as session:
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
+
+
+async def init_db():
+    """Create all tables. For development; use Alembic migrations in production."""
+    engine = get_engine()
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+
+
+async def close_db():
+    """Close the database engine."""
+    global _engine, _session_factory
+    if _engine is not None:
+        await _engine.dispose()
+        _engine = None
+        _session_factory = None