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

docs/project-structure.txt

@@ -200,6 +200,7 @@ Mana-Loop/
 │       │   │   ├── crafting-utils-recipe.test.ts
 │       │   │   ├── crafting-utils-time.test.ts
 │       │   │   ├── discipline-math.test.ts
+│       │   │   ├── discipline-prerequisites.test.ts
 │       │   │   ├── enemy-generator.test.ts
 │       │   │   ├── enemy-utils.test.ts
 │       │   │   ├── floor-utils.test.ts
@@ -248,6 +249,7 @@ Mana-Loop/
 │       │   │   │   ├── base.ts
 │       │   │   │   ├── elemental-regen-advanced.ts
 │       │   │   │   ├── elemental-regen.ts
+│       │   │   │   ├── elemental.ts
 │       │   │   │   ├── enchanter-special.ts
 │       │   │   │   ├── enchanter-spells.ts
 │       │   │   │   ├── enchanter-utility.ts