feat: add per-element mana regen disciplines for all 14 mana types

- Create data/disciplines/elemental-regen.ts (base + utility elements)
- Create data/disciplines/elemental-regen-advanced.ts (composite + exotic)
- Wire into ALL_DISCIPLINES via index.ts and discipline-slice.ts
- Add perElementRegenBonus to ComputedEffects type
- Merge regen_{element} discipline bonuses in computeAllEffects()
- Apply per-element regen to element mana each tick in gameStore
- Add 'Elemental Regen' and 'Advanced Regen' tabs to DisciplinesTab UI

docs/project-structure.txt

@@ -246,6 +246,8 @@ Mana-Loop/
 │       │   ├── data/
 │       │   │   ├── disciplines/
 │       │   │   │   ├── base.ts
+│       │   │   │   ├── elemental-regen-advanced.ts
+│       │   │   │   ├── elemental-regen.ts
 │       │   │   │   ├── enchanter-special.ts
 │       │   │   │   ├── enchanter-spells.ts
 │       │   │   │   ├── enchanter-utility.ts