fix(deps): add tailwind-merge to root package.json as direct dependency

turbo prune storefront --docker excludes admin, so tailwind-merge was
not installed at root in Docker (it was only hoisted because of admin's dep).
@heroui/styles/node_modules/tailwind-variants requires tailwind-merge >=3.0.0
and walks up to root to find it. Adding it as a root-level dep ensures npm ci
always installs it regardless of which workspace is being built.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package-lock.json

@@ -21,6 +21,7 @@
         "react-dom": "^19.2.4",
         "stripe": "^20.4.0",
         "svix": "^1.86.0",
+        "tailwind-merge": "^3.4.0",
         "tailwindcss": "^4.2.0"
       },
       "devDependencies": {

package.json

@@ -30,6 +30,7 @@
     "react-dom": "^19.2.4",
     "stripe": "^20.4.0",
     "svix": "^1.86.0",
+    "tailwind-merge": "^3.4.0",
     "tailwindcss": "^4.2.0"
   },
   "devDependencies": {