Don't detect mentions in code blocks

[judemont]

Description

fix: #2589
Don't detect mentions in code blocks and don't notify users.

Screenshots

Additional Context

Checklist

Are your changes backward compatible? Please answer below:

For example, a change is not backward compatible if you removed a GraphQL field or dropped a database column.
Yes, they are.
On a scale of 1-10 how well and how have you QA'd this change and any features it might affect? Please answer below:
8/10, I have manually tested

For frontend changes: Tested on mobile, light and dark mode? Please answer below:
N/A

Did you introduce any new environment variables? If so, call them out explicitly here:
No

Did you use AI for this? If so, how much did it assist you?
I used AI for the regex string.

[huumn]

@Soxasora would it be possible to use some of the editor tooling to pull out mentions/images etc? This regex stuff is brittle and we already do this robustly in the editor.

[Soxasora]

would it be possible to use some of the editor tooling to pull out mentions/images etc?

Yes, we can create a lexicalState on the spot (like with item creation, we can bundle lexicalState with item) or pick the one we use for items via DataLoader.
This opens a huge amount of possibilities, in this case we can either search nodes of type userMentionNode inside the lexicalState object or load this state on an headless editor and run lexical dollar functions such as $getNodesByType().

I need to continue the docs that I sadly de-prioritized for bugfixing, sorry about that!