Expand README with integration guides

[mmprotest]

Summary

• scaffold the raglite-sqlite package with MIT licensing, packaging metadata, and GitHub Actions CI
• implement the SQLite-backed RAG engine with parsers, chunking, embedding backends, hybrid search, and CLI commands
• add adapter utilities, export/statistics helpers, and pytest coverage for ingest/search flows and CLI smoke tests
• expand the README with advanced CLI tips plus LangChain and LlamaIndex integration examples

Testing

• not run (documentation-only change)

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https://chatgpt.com/codex/tasks/task_e_68de43afd5488331a336b8e1707b983d