feat(21-04): add subscription error handling with toast feedback on all pages

- Replace silent onError: () => {} with sticky toast notification
- Toast uses fixed ID 'sub-error' to prevent duplicate notifications
- duration: Infinity keeps toast visible until dismissed
- Applied to initiatives/index.tsx, initiatives/$id.tsx, inbox.tsx

packages/web/src/routes/initiatives/$id.tsx

@@ -3,6 +3,7 @@ import { createFileRoute, useNavigate } from "@tanstack/react-router";
 import { AlertCircle } from "lucide-react";
 import { Button } from "@/components/ui/button";
 import { Skeleton } from "@/components/Skeleton";
+import { toast } from "sonner";
 import { trpc } from "@/lib/trpc";
 import { InitiativeHeader } from "@/components/InitiativeHeader";
 import { ProgressPanel } from "@/components/ProgressPanel";
@@ -218,13 +219,23 @@ function InitiativeDetailPage() {
       void utils.listTasks.invalidate();
       void utils.listPlans.invalidate();
     },
-    onError: () => {},
+    onError: () => {
+      toast.error("Live updates disconnected. Refresh to reconnect.", {
+        id: "sub-error",
+        duration: Infinity,
+      });
+    },
   });
   trpc.onAgentUpdate.useSubscription(undefined, {
     onData: () => {
       void utils.listAgents.invalidate();
     },
-    onError: () => {},
+    onError: () => {
+      toast.error("Live updates disconnected. Refresh to reconnect.", {
+        id: "sub-error",
+        duration: Infinity,
+      });
+    },
   });
 
   // State