feat(FN-3711): consolidate graph position storage and remove scopedStorage

Consolidated graph position storage into a canonical shared helper (`projectStorage.ts`) with hardened persistence logic and removed the duplicate `scopedStorage` module. Updated integration tests and documented the canonical storage approach. A smaller fix (`FN-3628`) addressed mobile touch targets

Fusion-Task-Id: FN-3711

packages/dashboard/app/utils/__tests__/projectStorage.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it, beforeEach } from "vitest";
+import { beforeEach, describe, expect, it, vi } from "vitest";
 
 import {
   GLOBAL_STORAGE_KEYS,
@@ -115,6 +115,24 @@ describe("projectStorage", () => {
     expect(getScopedItem("kb-dashboard-working-branch-filter", "proj-3")).toBeNull();
   });
 
+  it("getScopedItem returns null when localStorage.getItem is unavailable", () => {
+    vi.stubGlobal("window", { localStorage: {} });
+    expect(getScopedItem("kb-dashboard-list-columns", "proj-abc")).toBeNull();
+    vi.unstubAllGlobals();
+  });
+
+  it("setScopedItem is a no-op when localStorage.setItem is unavailable", () => {
+    vi.stubGlobal("window", { localStorage: {} });
+    expect(() => setScopedItem("kb-dashboard-list-columns", "value", "proj-abc")).not.toThrow();
+    vi.unstubAllGlobals();
+  });
+
+  it("removeScopedItem is a no-op when localStorage.removeItem is unavailable", () => {
+    vi.stubGlobal("window", { localStorage: {} });
+    expect(() => removeScopedItem("kb-dashboard-list-columns", "proj-abc")).not.toThrow();
+    vi.unstubAllGlobals();
+  });
+
   it("has no overlap between global and project-scoped keys", () => {
     const globalSet = new Set(GLOBAL_STORAGE_KEYS);
     const overlap = PROJECT_STORAGE_KEYS.filter((key) => globalSet.has(key));