feat: implement skeleton loading screens for all views (Phase 3.5)

Created comprehensive skeleton components providing visual feedback during
data loading. This improves perceived performance and provides a better
user experience with consistent loading states across all views.

Changes:
- NEW: src/components/LoadingSkeletons.tsx (+105 lines)
  - SealedSecretListSkeleton - 5 placeholder rows
  - SealedSecretDetailSkeleton - title + sections + actions
  - SealingKeysListSkeleton - 2 certificate placeholders
  - CertificateInfoSkeleton - metadata lines
  - ControllerHealthSkeleton - chip + info layout
  - All use wave animation and realistic layouts

- UPDATED: SealedSecretList.tsx
  - Use loading state from useList() hook
  - Show skeleton during data fetch
  - Smooth transition to real data

- UPDATED: SealedSecretDetail.tsx
  - Replace Headlamp Loader with custom skeleton
  - Better layout matching
  - No layout shift

- UPDATED: SealingKeysView.tsx
  - Add loading state detection
  - Show skeleton for certificates
  - Professional loading UX

- UPDATED: ControllerStatus.tsx
  - Replace CircularProgress with skeleton
  - Match chip + info layout
  - Consistent with other components

Benefits:
- Improved perceived performance
- Reduced layout shift (skeletons match real components)
- Consistent loading experience (wave animation)
- Better user feedback during data loading

Build: 356.44 kB (98.01 kB gzipped) - +1.52 kB (+0.4%)
Time: 4.78s

Progress: 11/14 phases complete (79%)

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

headlamp-sealed-secrets/src/components/SealedSecretList.tsx

@@ -17,6 +17,7 @@ import { usePermission } from '../hooks/usePermissions';
 import { SealedSecret } from '../lib/SealedSecretCRD';
 import { SealedSecretScope } from '../types';
 import { EncryptDialog } from './EncryptDialog';
+import { SealedSecretListSkeleton } from './LoadingSkeletons';
 import { VersionWarning } from './VersionWarning';
 
 /**
@@ -39,7 +40,7 @@ function formatScope(scope: SealedSecretScope): string {
  * SealedSecrets list view component
  */
 export function SealedSecretList() {
-  const [sealedSecrets, error] = SealedSecret.useList();
+  const [sealedSecrets, error, loading] = SealedSecret.useList();
   const [createDialogOpen, setCreateDialogOpen] = React.useState(false);
   const { allowed: canCreate } = usePermission(undefined, 'canCreate');
 
@@ -110,6 +111,15 @@ export function SealedSecretList() {
     [canCreate, handleOpenDialog]
   );
 
+  // Show loading skeleton while data is being fetched
+  if (loading) {
+    return (
+      <SectionBox title="Sealed Secrets">
+        <SealedSecretListSkeleton />
+      </SectionBox>
+    );
+  }
+
   // Show error if CRD is not installed
   if (error) {
     return (