Move the UI test stack off Karma

[DerOetzi]

Why

Karma has been deprecated since April 2023, and the ecosystem has started to act on it.

• Jasmine announced the phase-out in jasmine/jasmine#2084: 6.x is the last version compatible with karma-jasmine, and 7.0 removed the APIs that only existed for it. Concretely, jasmine-core 7 ends its Env constructor with Object.freeze(this), while zone.js patches Jasmine by assigning to jasmine.getEnv().describe and friends in place. Every spec then fails to load with TypeError: Cannot assign to read only property 'describe' — see the closed bump build(deps-dev): Bump jasmine-core from 6.3.0 to 7.0.2 in /ui #593.
• zone.js is at 0.16.2, which is the newest release on npm, and it has no support for Jasmine 7.
• Angular's own builder announces it on every run: The "@angular-devkit/build-angular:karma" builder is deprecated as part of Angular's Webpack support deprecation.

So the UI test dependencies are frozen where they are: jasmine-core stays on 6.x, and .github/dependabot.yml ignores its majors until this issue is done. That is a holding position, not a plan.

What

Move ui/ to Angular's supported unit-test setup (@angular/build:unit-test, Vitest-based) and drop the Karma stack:

• angular.json: replace the test target's @angular-devkit/build-angular:karma builder.
• Remove karma, karma-chrome-launcher, karma-coverage, karma-jasmine, karma-jasmine-html-reporter, karma.conf.js and src/test.ts.
• Carry the coverage floor over. karma.conf.js currently enforces statements 68 / branches 53 / functions 56 / lines 67, and the rule is that work which adds coverage raises it to match — the replacement needs an equivalent gate, or CI loses it silently.
• .github/workflows/build_project.yml: check-ui runs npm test -- --watch=false --browsers=ChromeHeadlessCI --code-coverage; the flags change with the runner.
• Remove the jasmine-core ignore entry from .github/dependabot.yml.

Acceptance

• All 87 existing specs pass unchanged, or every deviation is explained.
• Coverage is enforced at no less than today's floor, and check-ui fails when it is undercut.
• No karma* package is left in ui/package.json.
• jasmine-core can move to its current major again, and the Dependabot ignore is gone.
• A decision record covers the runner choice.