feat: add API optimizations, cache invalidation and comprehensive test suite

- Add abort controllers and request deduplication to composables
- Add entity type cache invalidation on create/update/delete flows
- Add 179 new tests (utilities, services, composables, components)
- Fix Vue runtime warnings in structure editors

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/__mocks__/iconStub.ts

@@ -0,0 +1,12 @@
+/**
+ * Stub for ~icons/* imports (Unplugin Icons).
+ * Returns a minimal Vue component that renders a <span>.
+ */
+import { defineComponent, h } from 'vue'
+
+export default defineComponent({
+  name: 'IconStub',
+  render() {
+    return h('span', { class: 'icon-stub' })
+  },
+})