fix(m10): item-scope take-FX fingerprint; Windows path case-fold; comments

Item scope now reads the active take's FX chain via TakeFX_* (new
fxChainIdentityForItems helper), not the owning track's chain.
normalizeSlashes lowercases on _WIN32 for detectParent. Stale
comments corrected; case-fold tests added.

src/bank_model.h

@@ -44,8 +44,9 @@ struct SourceRange {
 };
 
 // Present only when a sample was resampled FROM another sample. Carries the
-// parent's id and the FX-chain snapshot string captured at resample time, so the
-// null-test / re-capture-from-source action (M10) can reconstruct the chain.
+// parent's id and the FX-chain snapshot string (a thin drift fingerprint, NOT a
+// restorable chunk) captured at resample time; the re-capture-from-source action
+// (M10) uses it to detect chain drift and replay the original capture request.
 struct Provenance {
     std::string parentSampleId;
     std::string fxChainSnapshot;