Overview

Switches JHipster generated projects to ESM by default:

• Adds "type": "module" in package.json.ejs for Angular, React, and Vue templates.
• Renames all .mjs.ejs template files to .js.ejs, including blueprint templates.
• Cleans up any leftover .mjs references in templates.

Verification

• Generated a new React app using the local generator:
  • package.json contains "type": "module"
  • No .mjs files remain outside node_modules
• Verified React and Vue templates generate correct ESM setup.

Related Issues

Fix #30509

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• All continuous integration tests are green
• Tests are added where necessary
• The JDL part is updated if necessary
• jhipster-online is updated if necessary
• Documentation is added/updated where necessary
• Coding Rules & Commit Guidelines as per our CONTRIBUTING.md document are followed

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