test: run the suite and benchmark with Bun's native test runner

Replace Vitest with bun test across the whole suite. A preload compiles
components through Angular's JIT transform with inlined templates, sets
up jsdom, TestBed and zoneless change detection, and a small shim covers
the Vitest APIs bun:test lacks. Files run isolated, real-worker specs
spawn the running Bun, and line coverage from lcov is converted to the
existing HTML and Cobertura reports. The CI benchmark replaces its heap
cap with a container memory limit. Vitest, Jest, Nx and their Vite
configuration are removed.

Refs #291

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

src/app/app-settings.spec.ts

@@ -7,7 +7,7 @@ import { MatOptionHarness } from '@angular/material/core/testing';
 import { MatDialogHarness } from '@angular/material/dialog/testing';
 import { MatSelectHarness } from '@angular/material/select/testing';
 import { MatSlideToggleHarness } from '@angular/material/slide-toggle/testing';
-import { type MockInstance, vi } from 'vitest';
+import { type MockInstance, vi } from '../testing/vitest-compat';
 import { App } from './app';
 import { CalendarService } from './services/calendar-service';
 import { calculatePlanningInternal } from './services/leave-planner.core';