build(deps-dev): bump tailwindcss from 3.4.19 to 4.2.1 in /apps/OpenSign

Bumps [tailwindcss](https://github.com/tailwindlabs/tailwindcss/tree/HEAD/packages/tailwindcss) from 3.4.19 to 4.2.1.
- [Release notes](https://github.com/tailwindlabs/tailwindcss/releases)
- [Changelog](https://github.com/tailwindlabs/tailwindcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/tailwindlabs/tailwindcss/commits/v4.2.1/packages/tailwindcss)

---
updated-dependencies:
- dependency-name: tailwindcss
  dependency-version: 4.2.1
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

apps/OpenSign/package.json

@@ -118,7 +118,7 @@
     "prettier": "^3.8.1",
     "pretty-quick": "^4.2.2",
     "rollup-plugin-node-polyfills": "^0.2.1",
-    "tailwindcss": "^3.4.19",
+    "tailwindcss": "^4.2.1",
     "tmp": "^0.2.5",
     "vite": "^7.3.1",
     "vite-plugin-svgr": "^4.5.0",