fix: resolve mana conversion, Spire/Grimoire tab errors, and legacy store references

- Fix mana conversion to deduct from regen instead of mana pool (resolves player stuck at 1 mana below cap)
- Fix Spire Tab error by removing unused legacy import (store-modules/enemy-utils)
- Fix Grimoire Tab error by adding Array.isArray check for effects.map
- Move utility functions from legacy store-modules to utils/ to eliminate legacy dependencies
- Add regression test for mana conversion fix
- Update SpellsTab.tsx imports to use utils instead of legacy stores

src/components/game/tabs/SpellsTab.tsx

@@ -5,7 +5,7 @@ import { GameCard, ElementBadge } from '@/components/ui';
 import { Badge } from '@/components/ui/badge';
 import { ELEMENTS, SPELLS_DEF } from '@/lib/game/constants';
 import { ENCHANTMENT_EFFECTS } from '@/lib/game/data/enchantment-effects';
-import { canAffordSpellCost } from '@/lib/game/stores';
+import { canAffordSpellCost } from '@/lib/game/utils';
 import { formatSpellCost, getSpellCostColor } from '@/lib/game/formatting';
 
 export function SpellsTab() {