feat(FN-3626): migrate plugin storage to project-scoped storage

Migrated the dependency-graph plugin's storage layer to use the project's scoped storage API (`projectStorage`) and added canonical storage-key assertions. The ChatView.tsx utility reference was updated to match the new storage path.

Fusion-Task-Id: FN-3626

packages/dashboard/app/utils/projectStorage.ts

@@ -29,6 +29,7 @@ export const PROJECT_STORAGE_KEYS: string[] = [
   "kb-usage-provider-order",
   "kb-chat-active-session",
   "kb-files-line-numbers",
+  "fusion-plugin-dependency-graph:positions",
 ];
 
 export function scopedKey(baseKey: string, projectId?: string): string {