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-special.ts

@@ -12,7 +12,7 @@ export const enchanterSpecialDisciplines: DisciplineDefinition[] = [
     manaType: 'death',
     baseCost: 22,
     description: 'Learn to enchant equipment with unique and powerful effects.',
-    statBonus: { stat: 'enchantPower', baseValue: 5 },
+    statBonus: { stat: 'enchantPower', baseValue: 5, label: 'Enchantment Power' },
     difficultyFactor: 220,
     scalingFactor: 130,
     drainBase: 4,