cpu-amx README: document the bf16 DiT tier (--dit-precision)

cpu-amx: add dit_medium_bf16_core.bin (bf16 DiT engine)

cpu-amx: add dit_medium_bf16_flash.so (bf16 DiT engine)

cpu-amx: add dit_medium_bf16_pin_fp32.npz (bf16 DiT engine)

cpu-amx: add dit_medium_bf16_core_manifest.txt (bf16 DiT engine)

cpu-amx: add dit_medium_bf16.so (bf16 DiT engine)

cpu-amx: add int8 encoders (same_{s,l}_encoder_int8, SmoothQuant+GPTQ) + README row

cpu-amx README: consistent <model>_<precision> filenames

cpu-amx: consistent <model>_<precision> filenames (t5gemma_bf16, dit_medium_int8, same_*_encoder_bf16)

Add cpu-amx: torch-free C++/AMX engines (T5Gemma bf16, medium DiT int8, SAME-S/L bf16+int8 decoders, SAME-S/L encoders) + weight blobs + README