fix(p15): remediate four green-minor review findings

Tokenize scrim navy RGB triple (--deepdrft-scrim-rgb); LAVA row now
flex-start so knobs group left; WAVE row keeps space-between for
right-pinned width knob; remove inert margin-left:auto/wvc-row-right;
correct stale seven->ten count in OnControlStateChanged comment.

DeepDrftShared.Client/wwwroot/styles/deepdrft-tokens.css

@@ -20,6 +20,10 @@
     /* Thin light-on-dark border, NowPlayingCard spirit (Phase 15 §5). One token instead of scattering
        the rgba(250,250,248,0.12) literal NowPlayingCard uses inline. */
     --deepdrft-border-light: rgba(250, 250, 248, 0.12);
+    /* Modal scrim base colour (RGB triple for use in rgba()) — panel dark-ground (#0D1B2A).
+       Deliberately NOT --deepdrft-navy (#112338); tokenised here so the scrim rule in
+       deepdrft-styles.css has no hardcoded literals. Change here once. */
+    --deepdrft-scrim-rgb: 13, 27, 42;
     /* Modal scrim opacity — the SINGLE point of truth for the visualizer-controls overlay tint
        (Phase 15 §4/§10.5). Mild so the panel reads as modal without a blackout. Change here once. */
     --deepdrft-modal-scrim-alpha: 0.3;