Can't import hex files generated from mkc CLI

[ssande-fwd]

Describe the bug
I'm trying to generate a MakeCode project in makecode.microbit.org from a hex file that was generated using mkc CLI. When I import the hex file it fails by saying "Sorry, we couldn't recognize this file".

To Reproduce
Steps to reproduce the behavior:

1. Generate a makecode project and hex file using mkc CLI
2. Import -> Import File... in https://makecode.microbit.org

Expected behavior
A MakeCode project is generated

Screenshots

Desktop (please complete the following information):

• OS: Windows 11
• Browser: Chrome
• Version: 143.0.7499.147

Additional Context
My colleague smartly pointed out that this is probably has something to do with the absence of main.blocks in CLI-generated projects, which is also causing the friction described in #6660.

[martinwork]

It looks like mkc generated hex files do not contain the embedded source that pxt CLI ones do - no 0E records at the end.