chore(deps): update build process for ESM-only @actions/core v3

[Copilot]

@actions/core v3 is ESM-only ("type": "module"), breaking the existing CommonJS build pipeline. The bundler (ncc) and test framework (Jest) failed to resolve ESM imports.

Changes

Package & TypeScript

• Added "type": "module" to package.json
• Updated tsconfig.json: module: "ES2022", esModuleInterop: true

Test Configuration

• Converted jest.config.js → jest.config.mjs with ts-jest ESM preset
• Added NODE_OPTIONS experimental-vm-modules flag
• Configured moduleNameMapper for @actions packages

Dependencies

• Replaced actions-toolkit (CommonJS) with @actions/github v9 (ESM)
• Updated getUserInfo() to use getOctokit() API

Build Output

• ncc now emits ESM bundle with lib/package.json type marker
• Renamed .prettierrc.js → .prettierrc.cjs for compatibility

// Before: actions-toolkit (incompatible)
const toolkit = new Toolkit({ secrets: [...] });
const res = await toolkit.github.users.getByUsername({username});

// After: @actions/github (ESM-compatible)
const octokit = getOctokit(getInput('github_token'));
const res = await octokit.rest.users.getByUsername({username});

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