Fix critical bugs, add test framework, improve code quality

- Fix syntax errors with missing brackets in store.ts and crafting-slice.ts
- Fix state mutation issues with lootInventory deep cloning
- Remove race condition from mid-tick set() call
- Fix COMBO_MASTER using wrong counter (totalTicks vs totalSpellsCast)
- Add null safety to hasSpecial() function
- Clamp mana to 0 in deductSpellCost() to prevent negative values
- Set up Vitest testing framework with 36 passing tests

src/lib/game/computed-stats.ts

@@ -386,11 +386,12 @@ export function deductSpellCost(
   const newElements = { ...elements };
   
   if (cost.type === 'raw') {
-    return { rawMana: rawMana - cost.amount, elements: newElements };
+    // Clamp to 0 to prevent negative mana
+    return { rawMana: Math.max(0, rawMana - cost.amount), elements: newElements };
   } else if (cost.element && newElements[cost.element]) {
     newElements[cost.element] = {
       ...newElements[cost.element],
-      current: newElements[cost.element].current - cost.amount
+      current: Math.max(0, newElements[cost.element].current - cost.amount)
     };
     return { rawMana, elements: newElements };
   }