Introduce EU7B v8 bake with global PROT chunk and v12 section payloads
(solo MODL + compact inst records, per-chunk solo/inst tables). Reader
parses v12 with chunked decode and v11→flat fallback; fix chunk blob
layout to write solo blocks before inst records.
Streaming: add unload keep-radius hysteresis on deceleration, ring-deficit
urgent drain, higher cold-mesh/apply budgets, and smarter warm-prefix
preload. Move UMES mesh prefetch to the main thread and route PACK apply
through ensure_pack_mesh_in_session_cache to avoid GetModel races on
Global.asCurrentTexturePath; harden MdlMngr texture-path trimming.
Rebake root scenario .eu7 files to get v12; existing v7–v11 packs remain
readable.