migrate group cards onto ClideCollapserCard; retire ClideHolderCard (T-305)

The activity run, edit run, and sub-agent run cards now render through the
shared ClideCollapserCard primitive instead of ClideHolderCard. The
collapsed ticker now leads with the card label, the count sits in a
fixed-width slot, and the status tick is pinned to the right edge.

ClideHolderCard (T-266) is fully superseded — removed along with its test
and golden; the deeper-control-passthrough coverage moved to the
ClideCollapserCard widget test.

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

CHANGELOG.md

@@ -194,6 +194,12 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Changed
 
+- The conversation stream's **collapsible cards** (activity runs, edit runs,
+  sub-agent runs) now share one `ClideCollapserCard` primitive with consistent
+  chrome: the collapsed ticker leads with the card's label, the step/edit count
+  sits in a fixed-width slot, and the status tick (spinner / check / cross) is
+  pinned hard against the card's right edge while the chevron hugs the left. A
+  `color` drives the border + label tint per card type. (T-305)
 - The Claude composer's **slash typeahead**, the team-chat **@-mention** list,
   and the status-bar **theme switcher** now ride the shared
   `ClideAnchoredOverlay` + `ClideMenu` popover primitive, alongside the menu