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/capture_paths.cpp

@@ -1,6 +1,7 @@
 #include "capture_paths.h"
 
 #include <cassert>
+#include <cctype>
 #include <cstdint>
 #include <cstdio>
 #include <cstring>  // std::memcmp
@@ -124,6 +125,13 @@ std::string normalizeSlashes(const std::string& path) {
     if (out.size() > 1 && out.back() == '/') {
         out.pop_back();
     }
+#ifdef _WIN32
+    // Windows paths are case-insensitive. Fold to lowercase so that two paths
+    // that differ only in drive-letter or component casing compare equal (e.g.
+    // "C:/Foo/BAR.wav" == "c:/foo/bar.wav"). On macOS/Linux, exact case is
+    // preserved (the filesystem is case-sensitive; folding would be wrong).
+    for (char& c : out) c = static_cast<char>(std::tolower(static_cast<unsigned char>(c)));
+#endif
     return out;
 }