feat: shift click to quick mention a user

[Asraye]

Adds an easy way to mention a user by pressing shift + click, on a username. Whether they're in the sidebar, a reply origin or just a general message!

Saw this in the "NOTES" and thought I'd take a crack, I tried a few different ways and found this to be the best approach with the least required changes and the least jank.

• Undepreciated: "Username", as we now use it to pass the UserId and handle the logic

How was this PR tested?

Tested locally with all edited areas (E.G: Replies, sidebar and messages - As seen in video)

Screenshots & Screencasts (if appropriate)

ShiftyClicky.mp4

Checklist:

• I have carefully read the contributing guidelines
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if applicable
• I have no unrelated changes in the PR
• I have confirmed that any new dependencies are strictly necessary
• I have written tests for new code (if applicable)
• I have followed naming conventions/patterns in the surrounding code

Please declare, if any, LLM usage involved in creating this PR

None; Just staying up past my sleepy time (I was meant to sleep 3 hours ago, I've spent 3 hours on this..)
...

Remember to Squash this into one commit... It took me two tries to fix lint.