feat(FN-3000): harden research lifecycle with idempotent cancel/retry and S

This merge hardens the research feature across the stack with idempotent cancel/retry logic and SSE support for real-time updates in `research-orchestrator` and `sse.ts`, while also applying UX improvements to `PlanningModeModal` and `ResearchTaskActionModal`. The core `research-store` received sign

Fusion-Task-Id: FN-3000

packages/dashboard/app/components/ResearchTaskActionModal.css

@@ -20,8 +20,6 @@
   flex-direction: column;
   gap: var(--space-xs);
   color: var(--text-muted);
-  font-size: 0.75rem;
-  letter-spacing: 0.03em;
   text-transform: uppercase;
 }
 
@@ -34,4 +32,22 @@
   .research-task-action-modal {
     width: min(100%, calc(100vw - (var(--space-md) * 2)));
   }
+
+  .research-task-action-modal__body {
+    gap: var(--space-lg);
+  }
+
+  .research-task-action-modal__preview {
+    padding: var(--space-lg);
+  }
+
+  .research-task-action-modal .modal-actions {
+    flex-direction: column;
+    align-items: stretch;
+    gap: var(--space-sm);
+  }
+
+  .research-task-action-modal .modal-actions .btn {
+    min-height: calc(var(--space-lg) * 2 + var(--space-xs));
+  }
 }