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.h

@@ -68,6 +68,10 @@ std::string hashWavContent(const std::vector<std::uint8_t>& bytes);
 
 // Normalizes a path to forward slashes and strips any trailing slash. Empty in
 // -> empty out. Pure string transform (does not consult the filesystem).
+// Platform case rule: on Windows (_WIN32) the result is also lowercased so that
+// paths differing only in drive-letter or component casing compare equal (Windows
+// paths are case-insensitive). On macOS/Linux the case is preserved exactly (those
+// filesystems are case-sensitive).
 std::string normalizeSlashes(const std::string& path);
 
 // Sanitizes a caller-supplied base name into a filesystem-safe stem: keeps