## Why

The analysis UI has three usability gaps: the two optimization modes ("Maximize Count" and "Priority Order") have minimal one-line descriptions that don't convey how they differ in practice, there is no visual loading feedback beyond a tiny per-set "analyzing..." label when the solver runs, and achieved specializations don't show their credit breakdown by default—users must discover the click-to-expand behavior on their own.

## What Changes

- Replace the terse one-line mode descriptions in `ModeToggle` with clearer, more informative explanations that help users understand the practical difference between the two algorithms.
- Add a skeleton loading placeholder to elective set cards while analysis is pending, replacing the minimal "analyzing..." text with a visual placeholder that communicates progress.
- Default achieved specializations to expanded state so users always see the per-course credit breakdown without needing to click.

## Capabilities

### New Capabilities
- `algorithm-explanations`: Improved descriptive text and presentation for the two optimization mode settings in ModeToggle.
- `analysis-skeleton-loading`: Skeleton placeholder UI shown on elective set cards while the decision tree worker is processing.
- `expanded-achieved-specializations`: Achieved specializations default to expanded, always showing the AllocationBreakdown credit list.

### Modified Capabilities

## Impact

- `app/src/components/ModeToggle.tsx` — updated descriptive text and possibly layout for mode explanations.
- `app/src/components/CourseSelection.tsx` — replace "analyzing..." text with skeleton loading placeholder.
- `app/src/components/SpecializationRanking.tsx` — change default expansion state for achieved specializations.