chore(claude): create triage command

[denolfe]

Adds a new /triage slash command to streamline the GitHub issue investigation workflow. This command automates the process of validating issues, identifying code locations, and determining next steps.

Usage: /triage <issue-number-or-url>

• Accepts issue number or URL as argument
• Fetches issue data via gh CLI
• Uses Explore agent for codebase investigation
• Generates structured triage report with validity verdict, confidence level, code locations, and fix direction
• Auto-saves findings to .claude/artifacts/triage-<issue-number>.md
• Offers post-triage options: create failing test, generate resolution plan, or complete