Pygin v57

v57 -- the last pure-HCE release. From here Pygin becomes an HCE/NNUE
hybrid, so this is the clean endpoint of the hand-crafted-eval line. Host
layer only: it plays exactly the same moves as v56 and reaches them the same
way, but it stops wasting time it has already earned.

Elo   | none claimed -- NODE-IDENTICAL to v56
SPRT  | no A/B slot spent (nothing to measure: same tree, same moves)
Conf  | ladder node-exact d1..d14, all search toggles at their v56 values
Games | 0
Penta | n/a
Split | n/a
Base  | vs Old Engine/56, ledger unchanged at +305
Bench | 1,145,629 nodes (unchanged -- the release is node-identical)

Time management

• Ponderhit now honours the soft-stop. A prediction hit used to spend the
  FULL fresh budget re-confirming a move it had already settled on -- the
  documented v1 deviation from when pondering shipped. It now applies the same
  P-35/U-06 fractions the main search uses. Measured 1.666s -> 0.686s, a ratio
  of 0.412 against the designed 0.40, so ~59% of that budget goes back on the
  clock for later moves.
• A latent bug fixed: the UCI layer restored a hardcoded 0.55 soft-stop
  fraction over whatever the engine itself set. Harmless today because the two
  agree -- but it meant any future soft-stop tuning would work in testing and
  be silently discarded in every real game.

UCI

• SoftStop, SoftStopStable, SoftStopUnstable, SoftStopStableIters --
  the time-policy neighbourhood, sweepable with no rebuild. Defaults are the
  shipped values, so an engine nobody configures is unchanged. SoftStop 0
  disables the soft-stop entirely.

Testing

• The frozen snapshots now carry their own engine.py. Old Engine/56 and
  57 were importing the LIVE one, which works only while it happens to
  match -- the next eval retune would have made every baseline silently adopt
  the new eval.

Self-contained binary -- no Python, no dependencies. Download, mark
executable, point your GUI at it.

Full Changelog: v56...v57