Unit testing the frontend (#7829)

This adds some unit tests for the front end.

- configures "frontend tests" as a unit tests in `static/tests`,
removing the old cypress-requiring "unit" tests
- hack enough of a DOM  to get things working
- port motd and id tests
- *adds* a golden layout checks  (see #7807)
- Updates READMEs etc

---------

Co-authored-by: Claude <noreply@anthropic.com>

package.json

@@ -111,12 +111,14 @@
     "css-minimizer-webpack-plugin": "^7.0.2",
     "cypress": "^14.4.1",
     "file-loader": "^6.2.0",
+    "happy-dom": "^18.0.1",
     "husky": "^9.1.7",
     "lint-staged": "^16.1.0",
     "mini-css-extract-plugin": "^2.9.2",
     "mock-fs": "^5.5.0",
     "monaco-editor-webpack-plugin": "^7.1.0",
     "nock": "^14.0.5",
+    "npm-run-all": "^4.1.5",
     "sass": "^1.89.2",
     "sass-loader": "^16.0.5",
     "source-map-loader": "^5.0.0",
@@ -156,7 +158,11 @@
     "update-browserslist": "npx browserslist@latest -- --update-db",
     "prepare": "husky",
     "ts-compile": "tsc",
-    "ts-check": "tsc -p ./tsconfig.backend.json --noEmit && tsc -p ./tsconfig.frontend.json --noEmit && tsc -p ./tsconfig.tests.json --noEmit",
+    "ts-check": "npm-run-all ts-check:*",
+    "ts-check:backend": "tsc -p ./tsconfig.backend.json --noEmit",
+    "ts-check:frontend": "tsc -p ./tsconfig.frontend.json --noEmit",
+    "ts-check:tests": "tsc -p ./tsconfig.tests.json --noEmit",
+    "ts-check:frontend-tests": "tsc -p ./tsconfig.frontend.tests.json --noEmit",
     "webpack": "node --no-warnings=ExperimentalWarning --import=tsx ./node_modules/webpack-cli/bin/cli.js --node-env=production --config webpack.config.esm.ts"
   },
   "license": "BSD-2-Clause",