Add skeleton loader - In honor of Halloween! 💀 🎃

[ullbergm]

👻 Spooky Scary Skeletons!

This PR adds a skeleton loader to give users a spook-tacular loading experience - just in time to celebrate Halloween (which was only a few days ago)! 🎃

🦴 What's New

• Skeleton Loader Component: Shows realistic loading placeholders while fetching applications and bookmarks
• Theme-Aware: Respects light/dark mode and overlay opacity settings
• Text-Length Based: Uses actual app names and descriptions to calculate skeleton widths for ultra-realistic sizing
• Selective Features: Tags appear on 25% of items, status badges on 10% - just like real apps
• Category Support: Organized by actual categories (Home Automation, Infrastructure, Productivity)
• Accessibility: Proper ARIA labels and screen reader support

🎃 Implementation Details

Component Architecture:

• Uses actual Application and ApplicationGroup components with skeleton={true} prop
• Perfect visual matching because it's the same components, just in "preview mode"
• Description skeletons render as individual word-like blocks based on real word lengths

Real Mock Data:

// Home Automation (3 apps)
- home assistant, node-red, vacuum

// Infrastructure (9 apps)  
- openshift, emqx, gatus, github repo, gitops, kasten k10, 
  load balancer, synology, unifi

// Productivity (3 apps)
- cyberchef, excalidraw, it-tools

Technical Highlights:

• Name width: nameLength * 8px (uppercase text)
• Description: Each word gets wordLength * 6px width
• Theme detection based on background preferences
• Respects all layout preferences (showDescription, showTags, showStatus, columnCount, etc.)

🧪 Testing

• ✅ All 9 SkeletonLoader tests passing
• ✅ All 354 frontend tests passing
• ✅ Spotless formatting applied
• ✅ Production ready (no debug delays)

🎭 Why "Skeleton" Loader?

Because what's Halloween without some friendly skeletons? This loader is here to make sure your users never see a dead page while waiting for data to load. It's a real no-brainer for improving perceived performance!

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This PR is dedicated to all the ghosts, ghouls, and skeletons who visited us this past Halloween. May your loading states be ever spooky! 👻💀🎃

[github-actions]

Test Results - JVM

943 tests  +9   935 ✅ +9   1m 8s ⏱️ -1s
 76 suites +1     8 💤 ±0 
 49 files   ±0     0 ❌ ±0 

Results for commit 58e1a1c. ± Comparison against base commit d01d819.

[github-actions]

Test Results - Native

943 tests  +9   935 ✅ +9   1m 6s ⏱️ ±0s
 76 suites +1     8 💤 ±0 
 49 files   ±0     0 ❌ ±0 

Results for commit 58e1a1c. ± Comparison against base commit d01d819.

[github-actions]

Pull Request closed and locked due to lack of activity.
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