route every tool use through the collapser (T-305 P3)

Every tool use now renders as a ClideCollapserCard over a one-item list
(a single tool is a list of one) — no separate single-card path. The
collapser carries the echoed last line, the count, and the aggregate
status (spinner while in-flight, check/cross once resolved); the inner
content card holds the call body + folded CALL/PROMPT/RESULT segments and
its own per-item mark. Inside a run (activity/edits/agent), tools render
as the bare inner content card so collapsers don't nest.

ConversationCard gains a `margin` param so inner cards carry no stream
margin; the collapser pads its inner canvas evenly on all sides (the
inner card no longer jams under the header). Rewrote the conversation_view
tests for the new structure and added a single-tool golden.

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

lib/widgets/src/clide_collapser_card.dart

@@ -187,8 +187,12 @@ class _ClideCollapserCardState extends State<ClideCollapserCard> {
               crossAxisAlignment: CrossAxisAlignment.stretch,
               children: [
                 _headerRow(tokens),
+                // Even padding around the inner item canvas (T-305): the sides +
+                // top match, and each inner item carries a matching bottom margin
+                // (so the last item's margin is the bottom inset and items in a
+                // multi-item run are evenly separated) — hence bottom 0 here.
                 Padding(
-                  padding: const EdgeInsets.fromLTRB(kClideCardHeaderPadH, 0, kClideCardHeaderPadH, 8),
+                  padding: const EdgeInsets.fromLTRB(kClideCardHeaderPadH, kClideCardHeaderPadH, kClideCardHeaderPadH, 0),
                   child: Column(
                     crossAxisAlignment: CrossAxisAlignment.stretch,
                     children: [