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>

docs/planner-cancellation.md

@@ -35,9 +35,9 @@ If Cancel is accepted just before a queued natural result reaches the facade, th
 Run the focused checks with the project's installed Bun and Node:
 
 ```sh
-bunx vitest run src/app/services/leave-planner-cancellation.spec.ts
-bunx vitest run src/app/services/leave-planner.worker.spec.ts
-bunx vitest run src/app/components/calendar-year/calendar-year-planning.spec.ts
+bun test --isolate src/app/services/leave-planner-cancellation.spec.ts
+bun test --isolate src/app/services/leave-planner.worker.spec.ts
+bun test --isolate src/app/components/calendar-year/calendar-year-planning.spec.ts
 bunx tsc --noEmit -p tsconfig.app.json
 bunx tsc --noEmit -p tsconfig.spec.json
 ```