fix(explorer): review follow-ups for #830 render-loop fix

- Wire the Explorer frontend's node --test suites (test:graph-store,
  test:graph-workspace, and the new test:plugin-registry regression
  test) into CI. Previously only `npm run build` ran, so none of the
  frontend tests -- including this fix's own regression coverage --
  executed anywhere except a contributor's local machine.
- Broaden the diagnostics dedup's structureLayer comparison to also
  cover disabledReason/curveCount/bridgeCurveCount/backboneCurveCount,
  not just cacheKey/lastDrawAt/enabled, so a disabledReason-only
  transition doesn't leave the dev diagnostics panel stale.

.github/workflows/ci.yml

@@ -30,11 +30,18 @@ jobs:
           node-version: '20'
           cache: 'npm'
           cache-dependency-path: explorer/package-lock.json
-      - name: Build Explorer frontend
+      - name: Install Explorer frontend dependencies
+        working-directory: explorer
+        run: npm ci
+      - name: Test Explorer frontend
         working-directory: explorer
         run: |
-          npm ci
-          npm run build
+          npm run test:graph-store
+          npm run test:graph-workspace
+          npm run test:plugin-registry
+      - name: Build Explorer frontend
+        working-directory: explorer
+        run: npm run build
       - run: pip install build
       - run: python -m build
       - name: Verify Explorer frontend is packaged