fix: Zustand selector anti-pattern causing infinite re-render + plugin loader path

- Fix usePluginStore(s => s.getAll*()) selectors that returned new arrays
  on every call, causing infinite re-render loops and permanent spinner
- Affected: Sidebar, Settings, ContactDetail, ContactEditModal, PluginRouteRenderer
- Use usePluginStore(s => s.manifests) + useMemo instead
- Fix PluginRouteRenderer: show spinner instead of null when manifests loading
- Fix PluginLoader: @/ path replacement ../ -> ../../ for correct dynamic imports

frontend/src/components/plugins/PluginLoader.tsx

@@ -40,8 +40,9 @@ function getLazyComponent(componentPath: string): React.LazyExoticComponent<Reac
     return componentCache.get(componentPath)!;
   }
 
-  // Convert @/pages/Mail to ../pages/Mail for dynamic import
-  const importPath = componentPath.replace(/^@\//, '../');
+  // Convert @/pages/Mail to ../../pages/Mail for dynamic import
+  // PluginLoader.tsx is in src/components/plugins/, so ../../ resolves to src/
+  const importPath = componentPath.replace(/^@\//, '../../');
 
   const LazyComp = lazy(() =>
     import(/* @vite-ignore */ importPath).then((m) => ({

frontend/src/components/plugins/PluginRouteRenderer.tsx

@@ -1,4 +1,6 @@
+import { useMemo } from 'react';
 import { useLocation } from 'react-router-dom';
+import { Loader2 } from 'lucide-react';
 import { usePluginStore } from '@/store/pluginStore';
 import { PluginPage } from './PluginLoader';
 
@@ -15,10 +17,15 @@ import { PluginPage } from './PluginLoader';
  */
 export function PluginRouteRenderer() {
   const location = useLocation();
-  const getAllPageRoutes = usePluginStore((s) => s.getAllPageRoutes);
+  const manifests = usePluginStore((s) => s.manifests);
   const loaded = usePluginStore((s) => s.loaded);
 
-  const routes = getAllPageRoutes();
+  const routes = useMemo(
+    () => manifests
+      .flatMap((m) => m.page_routes)
+      .sort((a, b) => a.order - b.order),
+    [manifests]
+  );
 
   // Find the first matching route (exact match or prefix match for nested routes)
   const matchedRoute = routes.find((r) => {
@@ -31,7 +38,6 @@ export function PluginRouteRenderer() {
 
   if (matchedRoute) {
     // Find the plugin name for display
-    const manifests = usePluginStore.getState().manifests;
     const plugin = manifests.find((m) =>
       m.page_routes.some((pr) => pr.path === matchedRoute.path)
     );
@@ -45,9 +51,13 @@ export function PluginRouteRenderer() {
     );
   }
 
-  // If manifests haven't loaded yet, show nothing (the static router handles it)
+  // If manifests haven't loaded yet, show a spinner (not null/blank)
   if (!loaded) {
-    return null;
+    return (
+      <div className="flex items-center justify-center min-h-[50vh]" role="status" aria-label="Loading">
+        <Loader2 className="animate-spin h-8 w-8 text-primary-500" aria-hidden="true" />
+      </div>
+    );
   }
 
   // No plugin route matched — show a simple not-found