Fix several MP/qsearch correctness bugs found by auditing ctx->uPly

indexing and per-thread state across MakeMove/recursion boundaries;
add a position-signature stamp so full-eval-only data can be validated
cheaply instead of approximated.

- chess.h/searchsup.c/search.c/root.c: add NODE_TYPE (PV/CUT/ALL)
  classification, set centrally in CommonSearchInit, replacing the old
  binary fPvNode flag. Fixes split.c's node-type check reading stale
  data on helper threads (they never call CommonSearchInit for the
  split-point ply) and removes a redundant, always-true parent-type
  check in search.c's own LMR gate.

- split.c: StartParallelSearch now copies the split point's eNodeType
  into SPLIT_INFO for helper threads to read (mirroring the existing
  iEval/iImprovement pattern); a split-node fail-high is now detected
  explicitly in search.c's move loop instead of falling through to the
  generic no_more_moves classifier, which misread it as a fail-low
  (skipping killer/history updates and storing an inverted-sense upper
  bound instead of a lower bound); ThreadUnderTerminatingSplit now
  checks all nested split pointers instead of just the first, so a
  thread notices when an inner split terminates while it's still
  helping an outer one; MAX_SPLITS bumped 20->64 for higher thread
  counts.

- chess.h/searchsup.c/search.c: convert
  SEARCHER_THREAD_CONTEXT.uLastPositionalSource (a single per-thread
  scalar) to PLY_INFO.uLastPositionalSource (per-ply). The scalar
  version was clobbered whenever QSearch's own move loop recursed
  before a later iteration read it back, corrupting which qsearch
  futility margin got applied; also fixes the same hazard in the
  newly-added check-evasion futility prune.

- chess.h/generate.c/searchsup.c: generalize move-scoring interpretation
  via a new MOVE_SCORING_SCHEME tag (per-ply, set by whichever
  generate.c routine last scored that ply's moves) and a single shared
  DecodeMoveValueEstimate, replacing scheme-blind decode logic in
  ComputeMoveScore and _ShouldWeConsiderThisMove.

- chess.h/eval.c/dynamic.c: stamp PLY_INFO.u64FullEvalSig with the
  position signature whenever a node completes a full (non-lazy) Eval()
  call. cEnprise/pEnprise/cTrapped/pTrapped/iKingScore/the eval-scoped
  bb*Attacks bitboards are only valid when this matches the position's
  live signature; _EnpriseSlotValid/_TrappedSlotValid now compare sigs
  directly instead of re-checking piece identity on the live board.

- searchsup.c: CommonSearchInit clears pi->mvBest on both its IsDraw and
  too-deep early-exit paths to prevent a later sibling node from reading
  stale mvBest data left by an unrelated earlier visit to the same ply.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01C9r36BydPnfpyYLFhkTo6d

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