docs: Add push-all slash command documentation and screenshot

- Add comprehensive push-all command documentation
- Include PR slash command screenshot
- Update .gitignore configuration
- Update slash commands README

🤖 Generated with Claude Code

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

.gitignore

@@ -43,3 +43,5 @@ yarn-error.log*
 # Temporary files
 *.tmp
 *.temp
+# Keep .claude/ clean for hand-on section
+.claude/