All-signal FSDB navigation warmup can exceed a 2GiB process cap

Follow-up to ffrSetLoadNavDBOnlyOnce benchmark: initialize every accepted ID1..max (81035) with a point view window. big.fsdb open/tree/select0.228s + first load2.627s + unload0.825s; whole two-window peak~0.755GiB RSS. huge.fsdb failed first load after22.45s under2GiB RLIMIT_AS, insufficient memory/SIGABRT, peak~1.75GiB RSS. This includes point-value setup and reconstruction, not pure navigation memory; no unconstrained requirement measured. Pinning a fixed8-signal cohort previously took~2s initially/~199MB and subsequent narrow-window cycles15-19ms. Prefer bounded cohorts over blindly initializing all IDs on shared hosts.