Fix packed INT8 resident-byte validation

[Alex-Wengg]

Summary

• validate mixed DiT resident bytes against the selected runtime profile
• accept the packed INT8 total of 1,829,712,128 bytes instead of incorrectly requiring the 3,150,917,888-byte FP16/K4 total
• add a behavioral regression test that constructs and owns the packed INT8 phase

Validation

• focused DiT backend test: 32 passed
• ACE-Step suite: 2,033 passed, 27 skipped
• web integration: 45 passed
• ACE-Step typecheck and production build passed

This fixes the live failure: ACE mixed DiT physical resident-byte replacement contract changed.