🔨 TASK-012: Add Loading States and Transitions

[ajacobm]

Task: Add Loading States and Transitions

Description: Add proper loading states and smooth transitions for view switching and data loading.

Technical Details:

• Add loading skeletons for cards
• Add transition animations for drill-down
• Show loading indicator during data fetch
• Animate view toggle transition
• Handle error states gracefully

Files to Create/Modify:

frontend/src/components/workbench/CardSkeleton.tsx    (create)
frontend/src/components/workbench/WorkbenchCanvas.tsx (modify - add loading states)
frontend/src/index.css                                 (modify - add transitions)

Loading States:

1. Initial Load: Skeleton cards while fetching
2. Drill-Down: Fade/slide transition to new level
3. View Toggle: Smooth crossfade between views
4. Error State: Friendly error message with retry

Acceptance Criteria:

• Skeleton loaders shown while loading
• Smooth fade/slide for drill-down
• View toggle animates smoothly
• Error states display helpful message
• No layout shift during loading

Effort: M (Medium - 4-8 hours)

Parent Story: #40
Parent Epic: #27

Branch: task/polish/loading-transitions