chore(deps): adopt senpi 2026.9.16-3 for the engine-free help screen

senpi 2026.9.16-3 (senpi#1758, senpi#1760) answers --help from a cache of
the last launch's extension flags before the engine module graph is
imported, and draws the startup spinner's first frame synchronously.
Measured with hyperfine on an Apple M4 Pro: the engine help with the omo
plugin drops from 1157 ms to 28 ms on bun and from 995 ms to 59 ms on
node; the reporter of #8371 measured 47.8 s on Windows.

Refs #8371