Rebase floor-tier Qwen residency
Two consecutive release-gate runs of the installed b10068 artifact reached a 4,140 MiB peak. The first run had 95 samples, including three consecutive 4,140 MiB samples post-multimodal; schema validation was 10/10 at 0.922 expected-content preservation.
Rebase arithmetic: 4,140 + 7 MiB cushion = 4,147.
Derived requirement: 4,147 + 2,947 + 1,024 = 8,118.
8 GiB headroom: 8,192 - 8,118 = 74 MiB.
Placement arithmetic and the b10068 pin are unchanged.