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/strategyHelpers/blueGreen/serviceBlueGreenHelper.test.ts

@@ -1,26 +1,26 @@
+import {vi} from 'vitest'
 import * as core from '@actions/core'
 import {
    BLUE_GREEN_VERSION_LABEL,
    getManifestObjects,
    GREEN_LABEL_VALUE
-} from './blueGreenHelper'
-import * as bgHelper from './blueGreenHelper'
-import {Kubectl} from '../../types/kubectl'
+} from './blueGreenHelper.js'
+import * as bgHelper from './blueGreenHelper.js'
+import {Kubectl} from '../../types/kubectl.js'
 import {
    getServiceSpecLabel,
    getUpdatedBlueGreenService,
    validateServicesState
-} from './serviceBlueGreenHelper'
+} from './serviceBlueGreenHelper.js'
 
 let testObjects
 const ingressFilepath = ['test/unit/manifests/test-ingress-new.yml']
-jest.mock('../../types/kubectl')
+vi.mock('../../types/kubectl')
 const kubectl = new Kubectl('')
 
 describe('blue/green service helper tests', () => {
    beforeEach(() => {
-      //@ts-ignore
-      Kubectl.mockClear()
+      vi.mocked(Kubectl).mockClear()
       testObjects = getManifestObjects(ingressFilepath)
    })
 
@@ -42,7 +42,7 @@ describe('blue/green service helper tests', () => {
       mockLabels[BLUE_GREEN_VERSION_LABEL] = bgHelper.GREEN_LABEL_VALUE
       const mockSelectors = new Map<string, string>()
       mockSelectors[BLUE_GREEN_VERSION_LABEL] = GREEN_LABEL_VALUE
-      jest.spyOn(bgHelper, 'fetchResource').mockImplementation(() =>
+      vi.spyOn(bgHelper, 'fetchResource').mockImplementation(() =>
          Promise.resolve({
             kind: 'Service',
             spec: {selector: mockSelectors},