feat(FN-1298): add stop-agent-run flow across engine and dashboard

- Add heartbeat stopRun support in the engine and wire it into the dashboard server lifecycle
- Add an agent run stop API route and client helper with route-level test coverage
- Add stop controls in AgentDetailView and AgentRunHistory with updated UI tests
- Add a changeset for @gsxdsm/fusion documenting the new stop run feature

packages/dashboard/src/server.ts

@@ -74,6 +74,7 @@ export interface ServerOptions {
   heartbeatMonitor?: {
     startRun(agentId: string, options?: { source: import("@fusion/core").HeartbeatInvocationSource; triggerDetail?: string; contextSnapshot?: Record<string, unknown> }): Promise<import("@fusion/core").AgentHeartbeatRun>;
     executeHeartbeat(options: { agentId: string; source: import("@fusion/core").HeartbeatInvocationSource; triggerDetail?: string; taskId?: string; contextSnapshot?: Record<string, unknown> }): Promise<import("@fusion/core").AgentHeartbeatRun>;
+    stopRun(agentId: string): Promise<void>;
   };
 }