Remove larql --version check; ubuntu-22.04 binary building now

Rebuild: binary is now at GitHub Releases (21 MB, pre-built on ubuntu-latest)

Simplified: download pre-built binary from GitHub Releases (no Rust build in image)

Fix: use system OpenBLAS (openblas-src system feature) — no from-source build

Fix: add libopenblas-dev, auto-download demo vindex from HF dataset on startup

Add LARQL Explorer: Gradio UI + Docker build

initial commit