feat(FN-2999): harden research lifecycle with idempotent cancel/retry, SSE

Merges FN-2999 research hardening (idempotent cancel/retry routes, aligned SSE event wiring, and cleaned status handling in the core research store and orchestrator) plus UI improvements to AgentDetailView header actions and planning disclosure UX in the modal, with a CSS token fallback fix in Scrip

Fusion-Task-Id: FN-2999

packages/cli/src/extension.ts

@@ -1306,10 +1306,9 @@ export default function kbExtension(pi: ExtensionAPI) {
         };
       }
 
-      researchStore.updateStatus(params.id, "cancelled", { cancelledAt: new Date().toISOString(), error: "Cancelled via extension" });
-      const updated = researchStore.getRun(params.id)!;
+      const updated = researchStore.requestCancellation(params.id);
       return {
-        content: [{ type: "text", text: `Marked research run ${params.id} as cancelled.` }],
+        content: [{ type: "text", text: `Requested cancellation for research run ${params.id} (status: ${updated.status}).` }],
         details: toResearchRunDetails(updated),
       };
     },