Paygent integration new with revert pipecat/realtime changes (#539)

* added paygent integration

* fix(paygent): resolve PR code review issues for cost tracking and billing

* docs(integrations): add Paygent integration guide

* docs(paygent): align step 1 with 3-step agent creation UI screenshots

* removed pipecat/realtime changes and review comments solved

api/services/integrations/paygent/node.py

@@ -0,0 +1,149 @@
+from __future__ import annotations
+
+from pydantic import model_validator
+
+from api.services.integrations.base import IntegrationNodeRegistration
+from api.services.workflow.node_data import BaseNodeData
+from api.services.workflow.node_specs._base import (
+    GraphConstraints,
+    NodeCategory,
+    NodeExample,
+    PropertyType,
+)
+from api.services.workflow.node_specs.model_spec import (
+    build_spec,
+    node_spec,
+    spec_field,
+)
+
+
+@node_spec(
+    name="paygent",
+    display_name="Paygent",
+    description="Cost Tracking and Billing",
+    llm_hint=(
+        "Paygent is a post-call usage-tracking and billing integration. "
+        "It does not participate in the conversation graph and should not be connected to other nodes."
+    ),
+    category=NodeCategory.integration,
+    icon="CreditCard",
+    examples=[
+        NodeExample(
+            name="paygent_tracking",
+            data={
+                "name": "Paygent Tracking",
+                "paygent_enabled": True,
+                "paygent_api_key": "pg_live_xxxxxxxxxxxxxxxx",
+                "paygent_agent_id": "my-voice-agent-prod",
+                "paygent_customer_id": "org-123",
+                "paygent_indicator": "per-minute-call",
+            },
+        )
+    ],
+    graph_constraints=GraphConstraints(
+        min_incoming=0, max_incoming=0, min_outgoing=0, max_outgoing=0, max_instances=1
+    ),
+    property_order=(
+        "name",
+        "paygent_enabled",
+        "paygent_api_key",
+        "paygent_agent_id",
+        "paygent_customer_id",
+        "paygent_indicator",
+    ),
+    field_overrides={
+        "name": {
+            "spec_default": "Paygent",
+            "description": "Short identifier for this Paygent configuration.",
+        },
+        "paygent_enabled": {
+            "display_name": "Enabled",
+            "description": "When false, Dograh skips all Paygent tracking for this call.",
+        },
+        "paygent_api_key": {
+            "display_name": "Paygent API Key",
+            "description": "API key used to authenticate requests to the Paygent REST API.",
+            "required": True,
+        },
+        "paygent_agent_id": {
+            "display_name": "Agent ID",
+            "description": "The agent identifier registered in your Paygent account.",
+            "required": True,
+        },
+        "paygent_customer_id": {
+            "display_name": "Customer ID",
+            "description": "Your Paygent customer / organisation ID.",
+            "required": True,
+        },
+        "paygent_indicator": {
+            "display_name": "Indicator",
+            "description": "The indicator event name sent at the end of the call (e.g. per-minute-call).",
+            "required": True,
+            "spec_default": "per-minute-call",
+        },
+    },
+)
+class PaygentNodeData(BaseNodeData):
+    paygent_enabled: bool = spec_field(
+        default=True,
+        ui_type=PropertyType.boolean,
+        display_name="Enabled",
+        description="When false, Dograh skips all Paygent tracking for this call.",
+    )
+    paygent_api_key: str | None = spec_field(
+        default=None,
+        ui_type=PropertyType.string,
+        display_name="Paygent API Key",
+        description="API key used to authenticate requests to the Paygent REST API.",
+    )
+    paygent_agent_id: str | None = spec_field(
+        default=None,
+        ui_type=PropertyType.string,
+        display_name="Agent ID",
+        description="The agent identifier registered in your Paygent account.",
+    )
+    paygent_customer_id: str | None = spec_field(
+        default=None,
+        ui_type=PropertyType.string,
+        display_name="Customer ID",
+        description="Your Paygent customer / organisation ID.",
+    )
+    paygent_indicator: str = spec_field(
+        default="per-minute-call",
+        ui_type=PropertyType.string,
+        display_name="Indicator",
+        description="The indicator event name sent at the end of the call (e.g. per-minute-call).",
+    )
+
+    @model_validator(mode="after")
+    def _validate_enabled_config(self) -> "PaygentNodeData":
+        if not self.paygent_enabled:
+            return self
+
+        missing: list[str] = []
+        if not self.paygent_api_key or not self.paygent_api_key.strip():
+            missing.append("paygent_api_key")
+        if not self.paygent_agent_id or not self.paygent_agent_id.strip():
+            missing.append("paygent_agent_id")
+        if not self.paygent_customer_id or not self.paygent_customer_id.strip():
+            missing.append("paygent_customer_id")
+        if not self.paygent_indicator or not self.paygent_indicator.strip():
+            missing.append("paygent_indicator")
+
+        if missing:
+            fields = ", ".join(missing)
+            raise ValueError(
+                f"Paygent node is enabled but missing required fields: {fields}"
+            )
+
+        return self
+
+
+SPEC = build_spec(PaygentNodeData)
+
+NODE = IntegrationNodeRegistration(
+    type_name="paygent",
+    data_model=PaygentNodeData,
+    node_spec=SPEC,
+    sensitive_fields=("paygent_api_key",),
+)