Remove ctx->uPositional and the EVAL_HASH subsystem; fix GetRoughEvalScore.

Finishes work left half-done in 7857096 ("Replace ctx->uPositional with
a data-calibrated Eval() return value"): that commit added Eval()'s new
piPositional out-param but never migrated GetRoughEvalScore onto it, so
GetRoughEvalScore's mid/deep-tree fallback kept reading the old
ctx->uPositional field -- a per-thread EWMA written only on full-eval
calls and never touched by the (far more common) lazy-eval path, so it
carried a stale value from whatever unrelated position last triggered a
full eval, potentially many nodes/plies away. Combined with EVAL_HASH
being long since disabled (its probe branch already dead), every
GetRoughEvalScore call past ply 4 was effectively "material + garbage."

Fixed by having GetRoughEvalScore just call Eval() directly -- its own
lazy-exit machinery already is the cheap, calibrated estimate this
function exists to provide, so there's no separate estimator to
maintain. Removed ctx->uPositional entirely (struct field, its EWMA
update in eval.c, both root.c init sites, split.c's cross-split
propagation, testeval.c's reset) along with the entire EVAL_HASH
subsystem (struct, table, Probe/StoreEvalHash, main.c's now-dead
reporting branch, the GNUmakefile flag) -- confirmed unused elsewhere
and explicitly being cut for good, not coming back in this form.

Also fixed GetRoughEvalScore's prototype being wrongly declared inside
#ifdef EVAL_HASH in chess.h even though the function itself is defined
and called unconditionally -- this was the source of the recurring
"call to undeclared function 'GetRoughEvalScore'" implicit-declaration
warning seen throughout this session's builds.

Separately, fixed QSearch to match its own documented intent: the
en-prise/trapped-piece "don't let this side stand pat" check now only
fires if the side hasn't already been allowed to stand pat earlier in
this qsearch line (matching the comment above it, which already said
this but the code never implemented it).

Verified against baseline/typhoon_baseline (pristine, pre-session) on
ecm_ringers.ep_ (4), ecm_hard_quick.ep_ (50-sample), and
ecm_confident_quick.ep_ (40) at sn=5M, --cpus 1, book disabled:
pristine baseline solves 3/50 on the hard sample; this commit solves
6/50, with the stand-pat fix and GetRoughEvalScore fix each
contributing +1 independently confirmed. No regressions on the other
two suites (4/4 and 40/40 unchanged throughout).

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01YGSMkwjqiCk4XhbfN7ugD2

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