fix: close Θ-W7-T1 review — scaling guard, opacity claims, two vacuous test fixes

Guards the stroke blend against LICE_EXT_GET_SCALING, tightens the analytic-stroker's boxes and NaN handling, corrects the opaque-core threshold and inner-dial rationale in the docs, and re-derives two review-flagged tautological tests so they actually fail against the bugs they claim to catch.

src/shell/instrument/editor_internal.h

@@ -117,7 +117,7 @@ inline void drawTitleBand(LICE_IBitmap* bmp, const instrument::ui::Rect& title,
 inline constexpr float kKnobTrackArcPx = 1.0f;
 inline constexpr float kKnobValueArcPx = 3.0f;
 inline constexpr float kInnerDialArcPx = 2.0f;
-inline constexpr int kKnobNeedlePx = 2;
+inline constexpr float kKnobNeedlePx = 2.0f;
 
 // Draws one radial knob face: param_slider owns the value<->angle map; this turns it into
 // LICE calls. LICE takes radians, and drawing the 7->5 o'clock sweep through the top needs
@@ -162,8 +162,8 @@ inline void drawKnobFace(LICE_IBitmap* bmp, const instrument::ui::Rect& knobRect
     const double iy = kg.centerY + (tip.y - kg.centerY) * 0.35;
     const ui::Role needleRole = disabled ? ui::Role::TextDim : ui::Role::TextPrimary;
     strokeLineAA(bmp, static_cast<float>(ix), static_cast<float>(iy),
-                 static_cast<float>(tip.x), static_cast<float>(tip.y),
-                 static_cast<float>(kKnobNeedlePx), toLice(ui::roleColor(needleRole)));
+                 static_cast<float>(tip.x), static_cast<float>(tip.y), kKnobNeedlePx,
+                 toLice(ui::roleColor(needleRole)));
 }
 
 // The concentric INNER dial: a second value on the same cell, drawn in the categorical