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/provenance.h

@@ -46,13 +46,14 @@ enum class ProvenanceScope {
     Track,
 };
 
-// One FX-chain entry as the shell reads it from REAPER (TrackFX_GetFXName /
-// TrackFX_GetFXGUID / TrackFX_GetEnabled). Plain data — the shell fills it, the
+// One FX-chain entry as the shell reads it from REAPER. For Track scope the shell
+// uses TrackFX_GetFXName/GetFXGUID/GetEnabled; for Item scope it uses the TakeFX_*
+// equivalents over the active take's FX chain. Plain data — the shell fills it, the
 // pure fold turns the vector into the identity string.
 struct FxIdentityEntry {
-    std::string name;     // TrackFX_GetFXName
-    std::string guid;     // TrackFX_GetFXGUID -> guidToString (per-instance identity)
-    bool        enabled;  // TrackFX_GetEnabled
+    std::string name;     // TrackFX_GetFXName / TakeFX_GetFXName
+    std::string guid;     // TrackFX_GetFXGUID / TakeFX_GetFXGUID -> guidToString
+    bool        enabled;  // TrackFX_GetEnabled / TakeFX_GetEnabled
 };
 
 // The recorded capture recipe + source FX-chain identity — the thin fingerprint.
@@ -138,8 +139,9 @@ struct BankFileRef {
 //
 // Returns the parent sample id, or nullopt when the capture is not a genuine
 // resample-from-sample. Comparison is exact path identity; the caller normalizes
-// both sides identically so a slash/case difference never spuriously matches or
-// misses (case handling is the caller's normalization contract, not decided here).
+// both sides identically via normalizeSlashes (which lowercases on Windows) so a
+// slash/case difference never spuriously matches or misses. On Windows both sides
+// are lowercased before they reach here; on macOS/Linux they are case-exact.
 std::optional<std::string> detectParent(
     const std::vector<std::string>& sourceItemFiles,
     const std::vector<BankFileRef>& bankFiles);