fix(instrument-ui): distinguish Disabled from Off, add hover cue to mode toggles, close review minors

Adds a hairline outline for Disabled chrome buttons, resolves Hover on the four
mode-selector single-buttons, re-measures the control-surface doc's 1.2 layout
table post-reflow, and adds a structural test pinning every enable/mode toggle
to a derived segment.

src/shell/instrument/editor_paint_deck.cpp

@@ -135,10 +135,13 @@ void ReaSamplerEditor::paintDeck(LICE_IBitmap* bmp, const FaceLayout& fl) {
                         disabled ? Role::TextDim
                                  : (seg1Active ? Role::BgBase : Role::TextPrimary));
     };
-    // The single-button forms. ENABLE names what it controls and reads Primary on / dim gray
-    // off; MODE reads the current mode and has no off state. A control the MODE refuses draws
-    // Disabled, which is a third state and not a synonym for off: off is live and clickable,
-    // and the washed Disabled surface is what separates them.
+    // The single-button ENABLE form. Reads Primary on / dim gray off; a control the ENABLE
+    // gates draws Disabled, a third state and not a synonym for off (off is live and
+    // clickable). No deck ENABLE currently drives `disabled` true through this path — the
+    // deck's one Disabled control (FILTER's Band|Notch law when the filter itself is off)
+    // stays segmented and draws through `drawToggle` above — but the parameter stays for
+    // parity with that segmented form and because a future ENABLE could plausibly gate on
+    // something else the way Loop (chrome) already does outside this deck.
     const auto drawButtonToggle = [&](const DeckToggleLayout& t, const char* label, bool active,
                                       bool disabled) {
         const bool hov = !disabled && isHovered(HoverKind::kControl, t.id);
@@ -151,9 +154,19 @@ void ReaSamplerEditor::paintDeck(LICE_IBitmap* bmp, const FaceLayout& fl) {
                         active && !disabled ? Role::BgBase
                                             : (hov ? Role::TextPrimary : Role::TextDim));
     };
+    // The single-button MODE form: the label reads the current mode, so there is no off state
+    // and no dim-gray rest — it is always "on". Filled by accent/primary rather than routed
+    // through drawButtonToggle (which would force InteractionState::Active regardless of hov,
+    // leaving MODE with no hover cue at all): Hover mixes toward accent/hot FROM whatever base
+    // roleColorState is handed, so passing accent/primary here is what lets the already-lit
+    // button visibly brighten on hover instead of a hover mix nobody would notice against
+    // bg/cell's dark base.
     const auto drawModeToggle = [&](const DeckToggleLayout& t, EnvMode mode) {
-        drawButtonToggle(t, mode == EnvMode::Spline ? "Spline" : "Stage", /*active=*/true,
-                         /*disabled=*/false);
+        const char* label = mode == EnvMode::Spline ? "Spline" : "Stage";
+        const bool hov = isHovered(HoverKind::kControl, t.id);
+        const InteractionState st = hov ? InteractionState::Hover : InteractionState::Active;
+        fillSurface(bmp, toKitBox(t.seg0), Role::AccentPrimary, st);
+        kitTextCentered(bmp, t.seg0, label, Font::Micro, Role::BgBase);
     };
     const bool anySpline = splineActive(play);
 
@@ -224,8 +237,9 @@ void ReaSamplerEditor::paintDeck(LICE_IBitmap* bmp, const FaceLayout& fl) {
         }
         kitText(bmp, g.caption, caption, Font::Micro, Role::TextDim);
 
-        // The gain-reduction lamp. ROUND, where the overlay radios in this same slot are
-        // square, so it reads as a lamp rather than a control.
+        // The gain-reduction lamp — MASTER's own corner slot, the one the env decks' overlay
+        // radios used to share before focus-by-click replaced them. ROUND, not square, so it
+        // reads as a passive readout rather than a control.
         if (g.captionRadio.id >= 0 && g.captionRadio.passive) {
             const Rect& rb = g.captionRadio.box;
             const float r = rb.width / 2.0f - 0.5f;