palette: enlarge the region title into WCAG large class; repoint the grabbed envelope handle off hue

Corrects theme.h's large-text thresholds, names accent/secondary's real
binding limiter, and adds compositeOver so the loop-span fill's 2.25:1
under-floor pair is asserted rather than assumed.

src/shell/panel/draw_kit.h

@@ -42,13 +42,14 @@ using ui::ListRowBox;
 using ui::Role;
 using ui::SliderGeometry;
 
-// The kit's four cached fonts. Consumers pass a Font to text() to pick the size/weight;
-// the kit maps it to the matching LICE_CachedFont.
+// The kit's cached fonts. Consumers pass a Font to text() to pick the size/weight; the kit
+// maps it to the matching LICE_CachedFont.
 enum class Font {
-    Title,      // ~15px semibold — region titles, headings
-    Label,      // ~12px regular — labels, body
-    ValueMono,  // ~12px tabular/mono — numbers (dB/ms/notes) that must not jitter
-    Micro,      // ~10px dim — units, counts, keybinding sub-labels
+    RegionTitle,  // 19px BOLD — text that must qualify as WCAG large-scale (3:1 floor)
+    Title,        // ~15px semibold — headings (BODY class: 4.5:1 floor)
+    Label,        // ~12px regular — labels, body
+    ValueMono,    // ~12px tabular/mono — numbers (dB/ms/notes) that must not jitter
+    Micro,        // ~10px dim — units, counts, keybinding sub-labels
 };
 
 // Horizontal text alignment for text(). Vertical is always centered in the rect (the kit's
@@ -58,7 +59,7 @@ enum class Align { Left, Center, Right };
 // The one place a pure KitColor becomes a LICE_pixel. Defined in draw_kit.cpp.
 LICE_pixel toLice(const KitColor& c);
 
-// Creates the four cached fonts once; idempotent. Segoe UI for title/label/micro,
+// Creates the cached fonts once; idempotent. Segoe UI for region-title/title/label/micro,
 // Consolas (tabular) for value-mono. No-op-safe: if font creation fails, text()
 // draws nothing rather than crashing.
 void kitFontsInit();