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/fabricator.ts

@@ -12,7 +12,7 @@ export const fabricatorDisciplines: DisciplineDefinition[] = [
     manaType: 'earth',
     baseCost: 10,
     description: 'Improve your ability to craft and maintain golems.',
-    statBonus: { stat: 'golemCapacity', baseValue: 2 },
+    statBonus: { stat: 'golemCapacity', baseValue: 2, label: 'Golem Capacity' },
     difficultyFactor: 150,
     scalingFactor: 80,
     drainBase: 4,
@@ -40,7 +40,7 @@ export const fabricatorDisciplines: DisciplineDefinition[] = [
     manaType: 'sand',
     baseCost: 12,
     description: 'Reduce material costs for crafting.',
-    statBonus: { stat: 'craftingCostReduction', baseValue: 15 },
+    statBonus: { stat: 'craftingCostReduction', baseValue: 15, label: 'Crafting Cost Reduction' },
     difficultyFactor: 180,
     scalingFactor: 90,
     drainBase: 6,