refactor(canvas): ProvisioningTimeout uses pruneStaleKeys helper

Follow-up to #2110 (which generalised pruneStaleKeys to Map<string, T>).
Identified by the simplify reviewer on that PR as the only other
in-tree caller of the same shape: `for (const id of map.keys()) { if
(!liveIds.has(id)) map.delete(id); }`.

Net: -3 lines, one less hand-rolled GC loop. No behaviour change —
the helper does exactly what the inline block did.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

canvas/src/components/ProvisioningTimeout.tsx

@@ -2,6 +2,7 @@
 
 import { useState, useEffect, useCallback, useRef, useMemo } from "react";
 import { useCanvasStore, type WorkspaceNodeData } from "@/store/canvas";
+import { pruneStaleKeys } from "./canvas/useCanvasViewport";
 import { api } from "@/lib/api";
 import { showToast } from "./Toaster";
 import { ConsoleModal } from "./ConsoleModal";
@@ -125,11 +126,7 @@ export function ProvisioningTimeout({
 
     // Remove tracking for nodes that are no longer provisioning
     const activeIds = new Set(parsedProvisioningNodes.map((n) => n.id));
-    for (const id of tracking.keys()) {
-      if (!activeIds.has(id)) {
-        tracking.delete(id);
-      }
-    }
+    pruneStaleKeys(tracking, activeIds);
 
     // Also remove from timedOut list if no longer provisioning, and
     // clear `dismissed` entries for workspaces that finished so a