Add production SigLIP 2 CPU deployment

[kstonekuan]

What changed

• add a restart-safe production Compose deployment with durable artifact mounts
• add image and Compose health checks
• explain the GPU-index/CPU-query use case and OpenAI-compatible client usage
• clarify SigLIP 2 compatibility and switch the repository to the MIT license

Why

The text-only query service needs a reproducible production deployment before it can replace the dedicated query GPU.

Validation

• cargo fmt
• cargo clippy --all-targets --all-features -- --deny warnings
• cargo test --all-features
• cargo machete --with-metadata --skip-target-dir
• Compose rendering, production Docker build, hadolint, and Markdown link checks