feat: implement OpenAI-compatible Realtime API with authentication and management features

- Added support for public Realtime API, including new routes for managing API keys and handling WebRTC connections.
- Introduced RealtimeApiKey model and associated CRUD operations for admin management of API keys.
- Implemented authentication mechanisms for API keys and client secrets.
- Enhanced environment configuration with new secrets for Realtime API.
- Created OpenAIRealtime session management and event processing for real-time interactions.
- Updated schemas and settings to accommodate new features and ensure compatibility with existing systems.

backend/db/models.py

@@ -389,6 +389,32 @@ class SiteSetting(Base):
     )
 
 
+class RealtimeApiKey(Base):
+    """Hashed deployment-level credential for the public Realtime API."""
+
+    __tablename__ = "realtime_api_keys"
+
+    id: Mapped[str] = mapped_column(String(40), primary_key=True)
+    name: Mapped[str] = mapped_column(String(128))
+    key_prefix: Mapped[str] = mapped_column(String(32), unique=True, index=True)
+    key_hash: Mapped[str] = mapped_column(String(64))
+    expires_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    last_used_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    revoked_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now()
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
+    )
+
+
 class WebhookDelivery(Base):
     """Immutable event snapshot plus its asynchronous delivery state."""