DEV: Clean up package.json files (#22349)

Motivation: aligning us with JS/Ember practices (runtime deps in `dependencies`, build/dev-time deps in `devDependencies`)

1. Move deps to devDeps where applicable (rule of thumb: it's a devDep unless it's required at runtime by the rails app or it's imported in the addon's code)
2. Remove unused dependencies and add missing ones (in addons)
3. Remove empty `repository` fields
4. Move `engines` and `ember` fields to the bottom

app/assets/javascripts/admin/package.json

@@ -7,7 +7,6 @@
   "keywords": [
     "ember-addon"
   ],
-  "repository": "",
   "scripts": {
     "build": "ember build",
     "lint:hbs": "ember-template-lint .",
@@ -15,10 +14,10 @@
     "start": "ember serve"
   },
   "dependencies": {
+    "discourse-common": "1.0.0",
     "ember-auto-import": "^2.6.3",
     "ember-cli-babel": "^7.26.11",
-    "ember-cli-htmlbars": "^6.2.0",
-    "xss": "^1.0.14"
+    "ember-cli-htmlbars": "^6.2.0"
   },
   "devDependencies": {
     "@babel/core": "^7.22.5",