fix(heartbeat): replace HEARTBEAT_OK token with virtual tool-call decision

nanobot/config/schema.py

@@ -228,11 +228,19 @@ class ProvidersConfig(Base):
     github_copilot: ProviderConfig = Field(default_factory=ProviderConfig)  # Github Copilot (OAuth)
 
 
+class HeartbeatConfig(Base):
+    """Heartbeat service configuration."""
+
+    enabled: bool = True
+    interval_s: int = 30 * 60  # 30 minutes
+
+
 class GatewayConfig(Base):
     """Gateway/server configuration."""
 
     host: str = "0.0.0.0"
     port: int = 18790
+    heartbeat: HeartbeatConfig = Field(default_factory=HeartbeatConfig)
 
 
 class WebSearchConfig(Base):