Add gh-web-fallback Claude Code hook for GitHub API guidance

[Jython1415]

Summary

• Adds a PreToolUse Claude Code hook that detects gh CLI commands in environments where gh is unavailable but GITHUB_TOKEN is present
• Provides proactive guidance to use the GitHub REST API with curl instead
• Includes a 5-minute cooldown to avoid repetitive suggestions
• Updated .gitignore to track .claude/ directory so hooks are shared with repo clones

Test plan

• Test in Claude Code Web environment where gh is unavailable
• Verify hook triggers when attempting gh commands
• Verify cooldown mechanism works (no repeated suggestions within 5 minutes)
• Verify hook doesn't trigger when gh CLI is available

Resolves #125