enlarge the activity-card run-status spinner (T-304)

At size 12 the rotating logo-mark spinner on in-progress collapser cards
read as a static speck. Add a clideIconHero (24) control-geometry token
and use it for ClideStatusIndicator on the collapser — the spinner now
reads as motion at a glance; the success check / error cross share the
size so the card doesn't jump when the run settles. Only call site is the
collapser, so other status surfaces are untouched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/widgets/src/spacing.dart

@@ -85,5 +85,10 @@ const double clideIconHitTarget = 16;
 /// Emphatic icon (standalone affordances, primary action glyphs).
 const double clideIconEmphatic = 18;
 
+/// Hero icon — large enough to read at a glance, e.g. the activity-card run
+/// status where the spinner must be legible as motion, not a static speck
+/// (T-304). Success/error glyphs share it so the card doesn't jump on settle.
+const double clideIconHero = 24;
+
 /// Standard control height (tab, button, list row).
 const double clideControlHeight = 28;