BEAM-native Avatar actor with typed actions and bounded tool execution.

Avatar asks a typed actor predictor for one action per turn. Tool results, including policy denials and execution errors, become structured observations for the next turn. A reserved Finish action or iteration exhaustion invokes a separate typed finalizer for the task signature. Each tool callback runs in an isolated unlinked task under :tool_timeout_ms; a timeout kills that task, records a terminal action observation, and proceeds directly to finalization.