Bump alpinejs from 3.15.11 to 3.15.12 in /backend

Bumps [alpinejs](https://github.com/alpinejs/alpine/tree/HEAD/packages/alpinejs) from 3.15.11 to 3.15.12.
- [Release notes](https://github.com/alpinejs/alpine/releases)
- [Commits](https://github.com/alpinejs/alpine/commits/v3.15.12/packages/alpinejs)

---
updated-dependencies:
- dependency-name: alpinejs
  dependency-version: 3.15.12
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

backend/package-lock.json

@@ -15,7 +15,7 @@
     "@tailwindcss/forms": "^0.5.11",
     "@tailwindcss/postcss": "^4.2.2",
     "@tailwindcss/typography": "^0.5.19",
-    "alpinejs": "^3.15.8",
+    "alpinejs": "^3.15.12",
     "postcss": "^8.5.8",
     "signature_pad": "^5.1.3",
     "tailwindcss": "^4.2.2",