07-context-compression.ipynb: Context Compression technique using Headroom.
Same RAG setup as notebooks 01-06 (Lilian Weng blog posts, Claude Sonnet,
OpenAI embeddings). Replaces GPT-4o-mini pruning/summarization with local
Headroom compress() — zero extra LLM calls, zero cost.
Ready to fork and PR to https://github.com/langchain-ai/how_to_fix_your_context
