Loop-crossfade-ux review fixes: parked-drag no longer fakes LOOP OFF, waveform label contrast fixed, hover memoizes its bank read

Also corrects the cap-area, em-dash, glyph-overhang and heuristic-comment findings noted in review.

src/core/ui/theme.h

@@ -104,6 +104,14 @@ inline constexpr double kLoopSpanFillAlpha = 0.20;
 // body floor Font::Micro answers to.
 inline constexpr double kCardNameScrimAlpha = 0.75;
 
+// The waveform mark caption/label scrim: bg/base composited at this alpha UNDER the loop-state
+// caption and the four mark labels, so text/dim (Font::Micro, body class) stays readable when
+// the envelope's accent/primary peak reaches into the label's rect. Higher than
+// kCardNameScrimAlpha because text/dim needs more cover than text/primary to clear the same
+// 4.5:1 body floor against the same lime worst case — test_theme.cpp composes this exact value
+// against accent/primary to pin the floor both roles answer to.
+inline constexpr double kWaveformLabelScrimAlpha = 0.90;
+
 // Relative luminance per WCAG 2.1 (sRGB linearization + 0.2126/0.7152/0.0722 weighting). Alpha
 // is ignored — a translucent overlay's effective color is the caller's to compose first
 // (compositeOver).