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/services/calendar-objectives.worker.spec.ts

@@ -4,7 +4,7 @@ import { tmpdir } from 'node:os';
 import { join, resolve } from 'node:path';
 import { promisify } from 'node:util';
 import { Worker as NodeWorker } from 'node:worker_threads';
-import { vi } from 'vitest';
+import { vi } from '../../testing/vitest-compat';
 import { createPlanningCalculation } from './leave-planner.service';
 import type { OptimizationPlanningRule } from './leave-planner.core';
 import { OPTIMIZATION_PRESETS } from './planning-objectives';
@@ -28,7 +28,13 @@ await import(${JSON.stringify(resolve('src/app/services/leave-planner.worker.ts'
 parentPort.on('message', (data) => globalThis.self.onmessage({ data }));
 `,
 		);
-		await promisify(execFile)('bun', ['build', entry, '--target=node', '--outfile', bundle]);
+		await promisify(execFile)(process.execPath, [
+			'build',
+			entry,
+			'--target=node',
+			'--outfile',
+			bundle,
+		]);
 	});
 
 	beforeEach(() => {