Restructure examples directory and improve document storage

[rejojer]

Summary

• Consolidate tests/ into examples/documents/, clean up .gitignore and README links
• Add line_count for markdown documents and reorder structure keys for consistency
• Lazy-load documents via _meta.json index with corruption recovery, cache PDF page text so queries don't need the original file
• Update demo script with __file__-based paths and add pre-shipped workspace for out-of-the-box experience

Test plan

• Run examples/openai_agents_demo.py and verify it works without downloading the PDF
• Index a new PDF and confirm lazy-load round-trips correctly
• Delete _meta.json and verify it rebuilds from individual doc JSONs

[claude]

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[rejojer]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

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