fix: stabilize mini skill card height and fix preview updates

**Issue 1: Buttons jumping around**
- Mini skill cards had variable height based on description text length
- Prev/Next buttons would shift position when switching skills

**Fix 1: Fixed height cards**
- Added `minHeight: '5.5rem'` to both addition and subtraction mini skill cards
- Buttons now stay in consistent position regardless of content

**Issue 2: Preview not updating on skill change**
- React Query cache wasn't invalidating when clicking prev/next buttons
- Query key was missing skill IDs for mastery+mixed mode

**Fix 2: Include skill IDs in query key**
- Added `currentAdditionSkillId`, `currentSubtractionSkillId`, `currentStepId` to query key
- Preview now regenerates when skills change in mastery mode

Files changed:
- `MasteryModePanel.tsx`: Fixed height for mini skill cards (5.5rem)
- `WorksheetPreview.tsx`: Added skill IDs to query key dependencies

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/app/create/worksheets/addition/components/WorksheetPreview.tsx

@@ -104,6 +104,10 @@ function PreviewContent({ formState, initialData, isDark = false }: WorksheetPre
       formState.displayRules, // Smart mode: conditional scaffolding
       formState.difficultyProfile, // Smart mode: difficulty preset
       formState.manualPreset, // Manual mode: manual preset
+      // Mastery mode: skill IDs (CRITICAL for mastery+mixed mode)
+      formState.currentAdditionSkillId,
+      formState.currentSubtractionSkillId,
+      formState.currentStepId,
       // Other settings that affect appearance
       formState.name,
       formState.pAnyStart,

apps/web/src/app/create/worksheets/addition/components/config-panel/MasteryModePanel.tsx

@@ -287,6 +287,9 @@ export function MasteryModePanel({ formState, onChange, isDark = false }: Master
                 border: '1px solid',
                 borderColor: isDark ? 'gray.600' : 'gray.300',
                 backgroundColor: isDark ? 'gray.600' : 'white',
+                minHeight: '5.5rem',
+                display: 'flex',
+                flexDirection: 'column',
               })}
             >
               <div
@@ -429,6 +432,9 @@ export function MasteryModePanel({ formState, onChange, isDark = false }: Master
                 border: '1px solid',
                 borderColor: isDark ? 'gray.600' : 'gray.300',
                 backgroundColor: isDark ? 'gray.600' : 'white',
+                minHeight: '5.5rem',
+                display: 'flex',
+                flexDirection: 'column',
               })}
             >
               <div