refactor(agent-runner): remove protocol_version from various components and update related documentation

src/langbot/pkg/agent/runner/descriptor.py

@@ -36,9 +36,6 @@ class AgentRunnerDescriptor(pydantic.BaseModel):
     plugin_version: str | None = None
     """Optional plugin version"""
 
-    protocol_version: str = '1'
-    """SDK protocol version, default '1'"""
-
     config_schema: list[dict[str, typing.Any]] = []
     """Configuration schema using DynamicForm format"""
 
@@ -69,4 +66,4 @@ class AgentRunnerDescriptor(pydantic.BaseModel):
 
     def supports_knowledge_retrieval(self) -> bool:
         """Check if runner supports knowledge retrieval."""
-        return self.capabilities.get('knowledge_retrieval', False)
+        return self.capabilities.get('knowledge_retrieval', False)