test: migrate from Karma and Jasmine to Vitest

Karma is deprecated and depends on braces, which has no patched release for GHSA-vfj7-8cjw-p6xm. Tests now run through the @angular/build unit-test builder with Vitest and jsdom. fakeAsync is replaced by Vitest fake timers, and zone.js is dropped because the zoneless app only loaded it for the Karma test polyfills.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package.json

@@ -70,15 +70,13 @@
     "express": "^5.2.1",
     "markdown-it": "^15.0.2",
     "rxjs": "~7.8.0",
-    "tslib": "^2.3.0",
-    "zone.js": "~0.16.2"
+    "tslib": "^2.3.0"
   },
   "devDependencies": {
     "@angular/build": "^22.2.1",
     "@angular/cli": "^22.2.1",
     "@angular/compiler-cli": "^22.2.1",
     "@types/express": "^5.0.6",
-    "@types/jasmine": "~6.0.0",
     "@types/node": "^25.7.0",
     "@types/showdown": "^2.0.6",
     "@typescript-eslint/eslint-plugin": "8.71.1",
@@ -92,17 +90,13 @@
     "eslint-plugin-promise": "7.3.0",
     "eslint-plugin-unused-imports": "4.4.1",
     "husky": "^9.1.7",
-    "jasmine-core": "~6.2.0",
-    "karma": "~6.4.0",
-    "karma-chrome-launcher": "~3.2.0",
-    "karma-coverage": "~2.2.0",
-    "karma-jasmine": "~5.1.0",
-    "karma-jasmine-html-reporter": "^2.3.0",
+    "jsdom": "^30.1.2",
     "postcss": "^8.5.29",
     "postcss-selector-parser": "^7.1.1",
     "prettier": "^3.8.1",
     "sharp": "^0.35.5",
     "typescript": "~6.0.3",
-    "typescript-eslint": "8.71.1"
+    "typescript-eslint": "8.71.1",
+    "vitest": "^5.0.3"
   }
 }