refactor(examples): use SMEM layout selectors

[ArthurinRUC]

Summary

• Replace hardcoded Hopper K_SW128 SMEM atoms in examples 11-14 with selector-based layout selection.
• Use CUTLASS ss_smem_selector in C++ and hopper_helpers.get_smem_layout_atom in CuTe DSL.
• Expand example 11 comments with byte_offset vs element_offset and Swizzle<3,4,3> vs 16-bit Swizzle<3,3,3> examples.

Validation

• Local: ruff check, py_compile, clang-format -n -Werror, git diff --check.
• G2-docker smoke: examples 11-14 C++ and CuTe DSL paths, including warpgroup_mma_multicast.py and warp_specialization_pipeline.py, all PASS at M=256, N=256, K=64.