fix(supervisor): add useToolHandler to fix streaming with SupervisorAgent

[guoyangzhen]

Problem

SupervisorAgent with streaming enabled crashes with:

Error: this.toolConfig.useToolHandler is not a function

Reported in #252. When SupervisorAgent sets up the lead agent's toolConfig in configureSupervisorTools(), it only provides tool and toolMaxRecursions — missing useToolHandler. When the lead agent (BedrockLLMAgent or AnthropicAgent) processes a streaming response containing tool_use blocks, the fallback handler references this.toolConfig.useToolHandler which is undefined.

Root Cause

The fallback handler in both BedrockLLMAgent and AnthropicAgent (streaming and non-streaming paths) has a bug:

const toolHandler = this.toolConfig.useToolHandler ?? (async (response, conversationHistory) => {
  if (this.isAgentTools(tools)) {
    return tools.toolHandler(...);
  }
  return this.toolConfig.useToolHandler(response, conversationHistory);  // ← undefined!
});

When useToolHandler is not set AND the instanceof AgentTools check fails (can happen with different module instances), the code calls undefined.

Fix

Primary — supervisorAgent.ts: Add proper useToolHandler to the toolConfig that delegates to AgentTools.toolHandler with the required getter methods. This ensures correct tool dispatch for both streaming and non-streaming.

Secondary — bedrockLLMAgent.ts and anthropicAgent.ts: Replace the dangling this.toolConfig.useToolHandler reference in the fallback handler with a clear error message.

Testing

1. Create a SupervisorAgent with BedrockLLMAgent lead agent + streaming enabled
2. Send a query that triggers tool use
3. Verify streaming completes without crash and tool results are properly dispatched to team agents