build: convert to ESM and take @actions/core 3 and @actions/github 9

The CJS bundle could not resolve @actions/core 3.x or @actions/github 9.x, both of
which are ESM-only. Converting the project to ESM unblocks both majors.

- package.json gains "type": "module". Relative imports now carry the explicit .js
  extensions NodeNext requires; tsc rejects the build without them.
- Bundling moves from @vercel/ncc to esbuild. ncc has no ESM output mode, as its
  --target flag sets the language target rather than the module format.
- The bundle banner injects createRequire. Bundled CommonJS dependencies lazily
  require() Node built-ins, which esbuild rewrites to a shim that throws in ESM
  scope unless a require binding exists in module scope.
- ncc type-checked as a side effect of bundling and esbuild does not, so an
  explicit typecheck script (tsc --noEmit) replaces it and runs in CI.
- dist/licenses.txt and dist/sourcemap-register.js were ncc-specific artifacts and
  are removed. A process.setSourceMapsEnabled(true) banner replaces the latter.
- eslint-plugin-import cannot follow NodeNext's .js to .ts mapping, so
  import/no-unresolved is disabled in favour of the typecheck script.
- commitlint.config.js becomes .cjs, as its module.exports would throw once the
  nearest package.json declares type: module.

The undici override is retained, as no @actions/* release reaches undici 7 alone.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: marknet15

.eslintrc.yml

@@ -10,7 +10,8 @@ ignorePatterns:
   - '!.*'
   - '**/node_modules/.*'
   - '**/dist/.*'
-  - '.github/commitlint.config.js'
+  - '.github/commitlint.config.cjs'
+  - 'esbuild.config.js'
 
 parser: '@typescript-eslint/parser'
 
@@ -35,6 +36,10 @@ rules:
     'eslint-comments/no-use': 'off',
     'eslint-comments/no-unused-disable': 'off',
     'import/no-namespace': 'off',
+    # NodeNext requires relative imports to carry a `.js` extension that resolves
+    # to a `.ts` source. eslint-plugin-import's node resolver cannot follow that
+    # mapping; `tsc --noEmit` (npm run typecheck) checks resolution accurately.
+    'import/no-unresolved': 'off',
     'no-console': 'off',
     'i18n-text/no-en': 'off',
     'no-constant-condition': 'off',

.github/commitlint.config.js .github/commitlint.config.cjs.github/commitlint.config.js renamed to .github/commitlint.config.cjs

@@ -21,4 +21,4 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:
-          commitlintRulesPath: ".github/commitlint.config.js"
+          commitlintRulesPath: ".github/commitlint.config.cjs"

.github/workflows/conventional-commits.yaml

@@ -26,5 +26,8 @@ jobs:
       - name: Lint
         run: npm run lint
 
+      - name: Typecheck
+        run: npm run typecheck
+
       - name: Test
         run: npm test