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/SpellsTab.tsx

@@ -105,7 +105,7 @@ export function SpellsTab() {
                         <div className="text-xs text-gray-500 italic">{def.desc}</div>
                       )}
                       
-                      {def.effects && def.effects.length > 0 && (
+                      {def.effects && Array.isArray(def.effects) && def.effects.length > 0 && (
                         <div className="flex gap-1 flex-wrap">
                           {def.effects.map((eff, i) => (
                             <Badge key={i} variant="outline" className="text-xs">

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() {

src/components/game/tabs/SpireTab.tsx

@@ -7,7 +7,7 @@ import { Mountain } from 'lucide-react';
 import type { ActivityLogEntry } from '@/lib/game/types';
 import { ELEMENTS, GUARDIANS, SPELLS_DEF, SKILLS_DEF } from '@/lib/game/constants';
 import { calcDamage } from '@/lib/game/stores';
-import { getEnemyName } from '@/lib/game/store-modules/enemy-utils';
+// Removed legacy import - getEnemyName not used in this component
 import { getActiveEquipmentSpells, getTotalDPS } from '@/lib/game/computed-stats';
 import { getUnifiedEffects } from '@/lib/game/effects';
 import { formatSpellCost, getSpellCostColor } from '@/lib/game/formatting';