Enable browser mode for graph-rendering specs

[Yicong-Huang]

Task Summary

Enable Vitest browser mode (Playwright-driven) for the specs that exercise jointjs paper geometry. Right now they run under jsdom with a stub SVG polyfill — enough for jointjs to instantiate, not enough to compute the graph layout the assertions depend on.

Currently affected

• workflow-editor.component.spec.ts — entire suite (JointJS Paper + External Module Integration, ~22 tests). Every assertion depends on real getScreenCTM / getBBox / pointer-event hit testing that the jsdom polyfill returns identity-only stubs for. Currently kept on the exclusion list with the "jointjs paper geometry" comment in tsconfig.spec.json and angular.json.

• drag-drop.service.spec.ts — 2 specific tests pinned with it.skip and a #4866 comment:

  • should find 3 input operatorPredicates and 3 output operatorPredicates for an operatorPredicate with 3 input / 3 output ports
  • should update highlighting, add operator, and add links when an operator is dropped

  Both rely on findClosestOperators, which queries SVG geometry. The other 4 tests in this file pass under jsdom and are running.

The earlier-listed monaco-related specs (code-debugger, code-editor, codearea-custom-template, time-travel, versions-list, operator-property-edit-frame) turned out to be blocked by infrastructure issues (CSS import, missing requestIdleCallback, stale TestBed shape), not jsdom layout. They were re-enabled in #4950.

Approach

Add Vitest browser mode via @vitest/browser + Playwright:

1. yarn add -D @vitest/browser playwright
2. Add a separate vitest.browser.config.ts (or per-target config) that opts in to browser mode and includes only the affected patterns:

   test: {
     browser: { enabled: true, provider: 'playwright', headless: true, name: 'chromium' },
     include: ['**/workflow-editor.component.spec.ts', '**/drag-drop.service.spec.ts'],
   }

3. Wire a second gui:test-browser target into angular.json so ng test keeps the fast jsdom default and a dedicated browser-mode run handles these specs.
4. Drop workflow-editor.component.spec.ts from the jsdom exclude lists; flip the 2 drag-drop it.skip back to it.
5. CI: add an ubuntu-only job (Playwright on macos/windows runners would multiply minute cost), cache the Playwright binary by version.

Definition of done

• workflow-editor.component.spec.ts runs under browser mode with passing assertions.
• The 2 drag-drop it.skip tests are flipped back to it and pass under browser mode.
• CI runs both default (jsdom) and browser-mode test targets; total wall-clock impact understood.
• Documentation note in frontend/README.md (or similar) explaining when to use browser mode.

Task Type

• Bug
• New Feature
• Refactor / Cleanup
• DevOps / Deployment / CI
• Testing / QA
• Documentation
• Performance
• Other