v0.5.0

Added

• GPU cast safety audit: SAFETY comments on all as u32 casts in GPU paths (mod.rs, cuda_backend.rs, wgpu_backend.rs, stde_gpu.rs). Added debug_assert! guards on user-provided direction/batch counts in stde_gpu.rs.
• #[must_use] annotations: 19 pure functions now carry #[must_use] (support module helpers, GPU codegen, solver wrappers, Laurent::zero/one).
• #![warn(missing_docs)]: enabled crate-wide. All public items — 35 OpCode variants, ~190 elemental methods across Dual, DualVec, Taylor, TaylorDyn, Laurent, struct fields, and trait methods — now have doc comments.

Changed

• Test decomposition: split tests/stde.rs (1630 lines, 76 tests) into 5 focused files: stde_core, stde_stats, stde_pipeline, stde_higher_order, stde_dense. All 76 tests preserved.
• Removed ROADMAP.md — all phases (0–5) complete.