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

vitest.config.ts

@@ -0,0 +1,17 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    environment: 'node',
+    globals: true,
+    setupFiles: ['./src/test/setup.ts'],
+    include: ['src/**/*.{test,spec}.ts'],
+    coverage: {
+      reporter: ['text', 'json'],
+      exclude: [
+        'node_modules/**',
+        'src/test/**',
+      ],
+    },
+  },
+});