Add BasicQueryEngine demo script

[River-Qinghao]

Motivation

• Provide a minimal, runnable example to visually verify BasicQueryEngine behavior by loading SCImago category data into a local SQLite DB and exercising query methods.

Description

• Add run_basic_query_demo.py which uses CategoryUploadHandler to push data/scimago.json into relational_basic_demo.db, registers a CategoryQueryHandler with BasicQueryEngine, and prints totals for getAllCategories, getAllAreas and a sample getEntityById lookup.

Testing

• No automated tests were executed for this change; the demo script was added and committed but not run automatically.

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Codex Task