- add case 32 to decode/prefill dispatch switch
- fix swiz_col out-of-bounds for HEAD_DIM=32: XOR mask now limited to chunk count (3 for 32, 7 for >=64) instead of always 7, which produced column offsets >= LD=32 and corrupted shared memory
- restructure decode dispatch to #ifndef/#else/#endif matching prefill
- split astrai/extension/__init__.py into loader.py (kernel .so discovery) and ops.py (wrapper functions + torch SDPA fallback); __init__.py now re-exports the public API
