Disable qsearch danger-detection (SideCanStandPat) as an experiment

Profiling (pmcstat, sampled) showed SideCanStandPat as the single
hottest leaf function in the engine, ahead of Eval itself -- not from
expensive logic (it's a 3-line signature/lock/lookup), but from sheer
call volume (~95% of the tree is qsearch) combined with a likely-cold
16MB global hash table probe and an uncontended-but-nonzero lock/unlock
pair paid on every call even single-threaded.

Disabling it entirely: real bench nps was flat (~1.53M vs ~1.57M,
within noise -- the earlier "1.2M->1.75M" bench reading was itself an
uncontrolled, noisy single comparison on this shared box, not a real
effect). But ECM (sn 4M) came back at 655/879, the best result of the
whole session (vs 650 baseline) -- suggests the danger-detection
heuristic may have been net-negative for search quality on balance,
forcing exhaustive no-stand-pat search in some positions where
standing pat was actually fine. Speed claim didn't hold up; the
tactical-quality result is a genuine, unexpected positive worth
investigating further.

Not yet validated in self-play -- pending a clean match run.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

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