feat(frontend): c2 tasks panel + history import (sprint 8 phase 2)

- Add getC2Tasks / listCallbackHistory / importC2 API functions + types
- useC2Tasks with 2500ms polling (stops when all tasks completed)
- useC2CallbackHistory, useImportC2 hooks
- C2TaskStatusBadge, C2TasksPanel (expandable output rows, polling indicator)
- C2CallbackPicker extracted as shared component (reused in both modals)
- ImportC2HistoryModal: 2-step callback picker → paginated history table
- SimulationFormPage: RT card + tasks panel share left grid column; Import C2 history button
- 37 new tests (api/c2, C2TasksPanel, ImportC2HistoryModal, SimulationFormPage panel visibility)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/C2TaskStatusBadge.tsx

@@ -0,0 +1,27 @@
+// Dedicated badge for Mythic task statuses — separate from simulation status badges.
+// submitted / processed → primary-soft (in-flight)
+// completed → success-soft
+// error* / fail* → warn-soft (task-level issue, not system error)
+// anything else → cloud / graphite (unknown/neutral)
+
+interface C2TaskStatusBadgeProps {
+  status: string;
+}
+
+function badgeClass(status: string): string {
+  const s = status.toLowerCase();
+  if (s === 'completed') return 'bg-success-soft text-success';
+  if (s.startsWith('error') || s.startsWith('fail')) return 'bg-warn-soft text-warn';
+  if (s === 'submitted' || s === 'processed') return 'bg-primary-soft text-primary-deep';
+  return 'bg-cloud text-graphite border border-hairline';
+}
+
+export function C2TaskStatusBadge({ status }: C2TaskStatusBadgeProps): JSX.Element {
+  return (
+    <span
+      className={`inline-flex items-center rounded-pill px-3 py-[4px] text-[12px] leading-[1.3] font-bold ${badgeClass(status)}`}
+    >
+      {status}
+    </span>
+  );
+}