Migrate to esbuild/Vitest and upgrade @actions/* to ESM-only versions (#492)

* Migrate build toolchain from ncc/Jest to esbuild/Vitest

Replace the legacy ncc/Jest/Babel build stack with a modern ESM toolchain:

Build:
- Replace @vercel/ncc with esbuild (--platform=node --target=node20 --format=esm)
- Add createRequire banner for CJS interop in ESM bundle
- Add "type": "module" to package.json
- Add tsc --noEmit typecheck script (esbuild strips types without checking)
- Add typecheck to husky pre-commit hook

Dependencies:
- Bump @actions/core@3, exec@3, io@3, tool-cache@4 (ESM-only)
- Replace jest/ts-jest/@babel/* with vitest@4

Tests:
- Convert 29 test files: jest.fn()→vi.fn(), jest.mock()→vi.mock(), jest.spyOn()→vi.spyOn()
- Fix vitest 4 compat: mockImplementation requires args, mock call tracking, await .rejects

CI:
- Update build step from ncc build → npm run build
- Update composite action to use npm run build

* Switch tsconfig to NodeNext module resolution

Change module/moduleResolution from ES2022/bundler to NodeNext/NodeNext
and target from ES2022 to ES2020.

- Add .js extensions to all relative imports across 59 source/test files
  (required by NodeNext module resolution)
- Add vitest/globals to tsconfig types array for global test API declarations

src/utilities/kubectlUtils.test.ts

@@ -1,6 +1,9 @@
+import {vi} from 'vitest'
+vi.mock('@actions/core')
+
 import * as core from '@actions/core'
 import {ExecOutput} from '@actions/exec'
-import {checkForErrors} from './kubectlUtils'
+import {checkForErrors} from './kubectlUtils.js'
 
 describe('Kubectl utils', () => {
    it('checks for errors', () => {
@@ -39,7 +42,8 @@ describe('Kubectl utils', () => {
       ).toThrow()
 
       // with warn behavior
-      jest.spyOn(core, 'warning').mockImplementation(() => {})
+      const warnSpy = vi.spyOn(core, 'warning').mockImplementation(() => {})
+      warnSpy.mockClear()
       let warningCalls = 0
       expect(() => checkForErrors([success], true)).not.toThrow()
       expect(core.warning).toHaveBeenCalledTimes(warningCalls)