Revert webpack-encore major bump from npm audit fix

The audit fix (presumably run with --force) jumped @symfony/webpack-encore
from ^4.6.1 to ^7.1.0, which requires @babel/core ^8.0.0 as a peer -
but @babel/core was left at ^7.25.0, so a clean `npm install` failed
outright with ERESOLVE. Since docker/setup.sh and docker/restart.sh
both run npm install unconditionally, this would have broken every
future deploy/rebuild.

Reverted webpack-encore (and the incidentally-downgraded
webpack-notifier) back to the versions that were actually working,
regenerated package-lock.json, and verified both `npm install` and
`npm run build` succeed cleanly.

package.json

@@ -12,7 +12,7 @@
   "devDependencies": {
     "@babel/core": "^7.25.0",
     "@babel/preset-env": "^7.25.0",
-    "@symfony/webpack-encore": "^7.1.0",
+    "@symfony/webpack-encore": "^4.6.1",
     "babel-loader": "^9.1.3",
     "core-js": "^3.37.1",
     "css-loader": "^7.1.2",
@@ -22,7 +22,7 @@
     "sass-loader": "^14.2.1",
     "webpack": "^5.95.0",
     "webpack-cli": "^5.1.4",
-    "webpack-notifier": "^1.11.1"
+    "webpack-notifier": "^1.15.0"
   },
   "dependencies": {
     "@popperjs/core": "^2.11.8",