Copying a note from the view version to an email in gmail loses formatting

### Is this a hackmd.io issue?

Yes, the bug happens on https://hackmd.io

### What's the problem
If I go to a note e.g. https://hackmd.io/@oidf-wg-authzen/wg-meeting-20240625 and I want to select all the note's text to copy it and email it, it only pastes text. It loses formatting.

#### Current behaviour

> Screenshot (optional)

Provide steps to reproduce:

1. Go to any note in the view-only mode.
2. Select some or all of the note's text
3. Copy the text (ctrl+c)
4. Go to your email client (gmail)
5. Paste the text (Ctrl+v) and observe that the formatting is missing

#### Expected behaviour

Formatting should be preserved.

#### Environment

I use HackMD on:

- Browser: Chrome 126.0.6478.127 (Official Build) (64-bit) (cohort: Stable)