Control scale: Button/IconButton primitives, two-height tokens, app-wide migration

styles/tokens.css

@@ -39,6 +39,14 @@
   /* Layout */
   --header-height: 48px;
 
+  /* Control scale (arch 09 §4) — every interactive control is one of exactly two
+     heights. 32px is THE control height: buttons, inputs, selects, segmented
+     controls, icon buttons — anything that sits in a toolbar or form row. 40px is
+     reserved for standalone primary CTAs (e.g. the library's Build Chart) and
+     modal footers. No other control heights exist; a third value is drift. */
+  --control-height: 32px;
+  --control-height-lg: 40px;
+
   /* Motion — productive only; neutralized under prefers-reduced-motion in base.css */
   --dur-fast: 70ms;
   --dur-fast-2: 110ms;