Hex 2.0: Reactivity, Graphs, and a little bit of Magic

Introduced a new reactive compute engine that models Hex projects as DAGs. This engine automatically infers dependencies between cells (Python and SQL) and triggers re-execution only for dependent downstream logic. This addresses issues of reproducibility, performance, and interpretability inherent in traditional notebook kernels. The Graph view visualizes these dependencies, and the 'Auto Run' mode ensures that only affected cells are re-computed.