feat: discipline UI improvements - stat labels, prerequisites, mana type tab

- Add player-friendly label field to statBonus in DisciplineDefinition
- Show prerequisite requirements on locked discipline cards
- Disable activate button for locked disciplines
- Restructure elemental attunement into dedicated 'Mana Types' tab
- Add checkDisciplinePrerequisites utility function
- Update store to enforce prerequisite checking on activation
- Split discipline-prerequisites tests into separate file

src/lib/game/data/disciplines/enchanter-utility.ts

@@ -12,7 +12,7 @@ export const enchanterUtilityDisciplines: DisciplineDefinition[] = [
     manaType: 'light',
     baseCost: 8,
     description: 'Learn to enchant equipment with utility effects.',
-    statBonus: { stat: 'studySpeed', baseValue: 0.05 },
+    statBonus: { stat: 'studySpeed', baseValue: 0.05, label: 'Study Speed' },
     difficultyFactor: 80,
     scalingFactor: 60,
     drainBase: 2,
@@ -50,7 +50,7 @@ export const enchanterUtilityDisciplines: DisciplineDefinition[] = [
     manaType: 'water',
     baseCost: 15,
     description: 'Learn to enchant equipment with mana-boosting effects.',
-    statBonus: { stat: 'maxMana', baseValue: 10 },
+    statBonus: { stat: 'maxMana', baseValue: 10, label: 'Max Mana' },
     difficultyFactor: 150,
     scalingFactor: 100,
     drainBase: 3,