docs(examples): GH_TOKEN is required for example 54's GitHub MCP, not optional

Without GH_TOKEN the example sends 'Authorization: Bearer ' (empty) and
the run fails with a misleading MCP 400. The default
api.githubcopilot.com/mcp/ endpoint requires authentication, so document
the token as required and show how to set it from the gh CLI.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: ling-senpeng13

examples/agents/54-software-bug-assistant.ts

@@ -10,7 +10,7 @@
  *   - Conductor server with AgentTool + MCP support
  *   - CONDUCTOR_SERVER_URL=http://localhost:8080/api as environment variable
  *   - CONDUCTOR_AGENT_LLM_MODEL=openai/gpt-4o-mini as environment variable
- *   - GH_TOKEN in environment (optional, for GitHub MCP)
+ *   - GH_TOKEN in environment (required for GitHub MCP; e.g. export GH_TOKEN=$(gh auth token))
  */
 
 import { Agent, AgentRuntime, agentTool, tool, mcpTool } from '@io-orkes/conductor-javascript/agents';