Add shared Icon primitive and controlled glyph vocabulary (Carbon, filled)

src/app/components/Icon.module.css

@@ -0,0 +1,30 @@
+/* Shared icon primitive (arch 09 §5). Icons are fill: currentColor SVG, so they
+   inherit the surrounding text colour and theme automatically. The size classes
+   map to the Carbon scale tokens; the glyph keeps its own rounded geometry and is
+   exempt from --radius (square chrome applies to chrome, not icons). */
+.icon {
+  display: inline-block;
+  flex: 0 0 auto;
+  fill: currentColor;
+  vertical-align: middle;
+}
+
+.sm {
+  width: var(--icon-sm);
+  height: var(--icon-sm);
+}
+
+.md {
+  width: var(--icon-md);
+  height: var(--icon-md);
+}
+
+.lg {
+  width: var(--icon-lg);
+  height: var(--icon-lg);
+}
+
+.xl {
+  width: var(--icon-xl);
+  height: var(--icon-xl);
+}