fix: add eslint-plugin-jest to root devDependencies

The @backstage/cli eslint-factory config references plugin:jest/recommended,
but eslint-plugin-jest was nested inside @backstage/cli/node_modules/ and not
hoisted to the root. Adding it to root devDependencies ensures ESLint can
resolve it from packages/backend/ and packages/app/.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: JoshLuedeman

backstage/package.json

@@ -36,6 +36,7 @@
     "@playwright/test": "^1.32.3",
     "@types/jest": "^30.0.0",
     "@types/node": "^25.4.0",
+    "eslint-plugin-jest": "^28.0.0",
     "node-gyp": "^10.0.0",
     "prettier": "^2.3.2",
     "typescript": "~5.4.0"

backstage/yarn.lock

@@ -18482,6 +18482,24 @@ __metadata:
   languageName: node
   linkType: hard
 
+"eslint-plugin-jest@npm:^28.0.0":
+  version: 28.14.0
+  resolution: "eslint-plugin-jest@npm:28.14.0"
+  dependencies:
+    "@typescript-eslint/utils": "npm:^6.0.0 || ^7.0.0 || ^8.0.0"
+  peerDependencies:
+    "@typescript-eslint/eslint-plugin": ^6.0.0 || ^7.0.0 || ^8.0.0
+    eslint: ^7.0.0 || ^8.0.0 || ^9.0.0
+    jest: "*"
+  peerDependenciesMeta:
+    "@typescript-eslint/eslint-plugin":
+      optional: true
+    jest:
+      optional: true
+  checksum: 10c0/da9c99dd8a1a80aa0c126ff4558882451dcee61b7e4c88e2407ac27d0c86fad2951384a4b037748e26f8743890b4628c6917b0760b01b7017c53fb29768584bc
+  languageName: node
+  linkType: hard
+
 "eslint-plugin-jest@npm:^28.9.0":
   version: 28.11.0
   resolution: "eslint-plugin-jest@npm:28.11.0"
@@ -29297,6 +29315,7 @@ __metadata:
     "@playwright/test": "npm:^1.32.3"
     "@types/jest": "npm:^30.0.0"
     "@types/node": "npm:^25.4.0"
+    eslint-plugin-jest: "npm:^28.0.0"
     node-gyp: "npm:^10.0.0"
     prettier: "npm:^2.3.2"
     typescript: "npm:~5.4.0"