Add context engineering curriculum tracks

[cody-carlson]

Summary

• Add a PPTX-first workshop deck with Markdown outline and speaker notes for token optimization and context engineering
• Add 1-hour, 2-hour, and 4-hour delivery tracks across Copilot CLI, VS Code, GitHub.com web chat, coding agent, and code review
• Add facilitator guidance, preflight checklist, surface matrix, and student worksheets for context inventory and instruction diet exercises
• Update existing labs to connect the five token optimization levers with context engineering practices and surface-specific tradeoffs

Validation

• git diff --check
• MarkItDown conversion of generated PPTX verified slide extraction and key content