refactor : merge Inventory_frontend submodule into frontend/ directory

Merges the full git history of Inventory_frontend into the monorepo
under frontend/. Removes the submodule in favor of a unified repo.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/vitest.config.ts

@@ -0,0 +1,22 @@
+import { defineConfig } from 'vitest/config'
+import { resolve } from 'node:path'
+import vue from '@vitejs/plugin-vue'
+
+const iconStub = resolve(__dirname, 'tests/__mocks__/iconStub.ts')
+
+export default defineConfig({
+  plugins: [vue()],
+  test: {
+    globals: true,
+    environment: 'happy-dom',
+    root: '.',
+    include: ['tests/**/*.test.ts'],
+  },
+  resolve: {
+    alias: [
+      { find: /^~icons\/.*/, replacement: iconStub },
+      { find: '~', replacement: resolve(__dirname, 'app') },
+      { find: '#imports', replacement: resolve(__dirname, 'tests/__mocks__/imports.ts') },
+    ],
+  },
+})