[FLINK-40035][runtime-web] Add Vitest smoke tests for the web-dashboard

[spuru9]

What is the purpose of the change

The web-dashboard has no automated tests — eslint and the production build were the only guardrails, so framework upgrades (Angular, ng-zorro) rely on manual testing. This adds a Vitest-based test setup with smoke-level component specs for high-traffic views, wired into the existing CI build (FLINK-40035).

Brief change log

• Wire Vitest via Angular's @angular/build:unit-test builder (the default unit-test runner in Angular 21; Karma is deprecated). Tests run in jsdom, so no browser is required in CI. Adds tsconfig.spec.json and src/test-setup.ts with the jsdom stubs ng-zorro / Angular CDK need (matchMedia, ResizeObserver, IntersectionObserver).
• Migrate the build and serve targets from @angular-devkit/build-angular:browser-esbuild to @angular/build:application and :dev-server, which the unit-test builder requires and which is the Angular 21 default. Build output stays flat under web/, so packaging is unchanged. Removes the now-unused @angular-devkit/build-angular.
• Add smoke specs (rendering + basic interactions) for the Overview statistic cards, the Task Manager list, and the Job Exceptions view.
• Add test / test:ci npm scripts and include test:ci in ci-check, so the specs run as part of the existing Maven frontend build.

Verifying this change

This change adds tests and can be verified as follows:

• npm run test:ci runs the Vitest suite — 6 specs across 3 components pass.
• npm run ci-check (lint + tests + production build) passes; the production ng build output remains flat under web/ (unchanged packaging layout), with no CommonJS dependency warnings.
• The dev-server proxy (npm run proxy) was verified against a stub backend on :8081: all REST roots — including subpaths and query strings such as /jobs/<jid>/flamegraph?type=FULL — are proxied, while /, main.js, styles.css, and the lazy chunk-*.js files are served by the local dev server with the correct content types. The ^-regex proxy key introduced in FLINK-40045 behaves identically under @angular/build:dev-server (same Vite matching semantics).
• Regenerating the NOTICE file against a production-only install (npm ci --omit=dev) confirms no NOTICE change is needed — only devDependencies change.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): yes (web-dashboard build/test tooling only — adds vitest, jsdom, @angular/build; migrates the build to @angular/build:application; removes @angular-devkit/build-angular)
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no (test infrastructure)
• If yes, how is the feature documented? not applicable

AI Usage Disclosure

• Claude Code

[flinkbot]

CI report:

• dfd0056 Azure: SUCCESS

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[spuru9]

@MartijnVisser Can you check this PR.
I have added only some minor tests to kick start the component testing. Will create some JIRAs for adding more module level tests in future. Would have been a longer PR for review.
Also after adding sufficient amount of component test, would also look into feasibility of playwright tests.