Replaces Twitter with X in project (Issue 403)

[marknoble]

SVGs were sourced here: https://about.x.com/en/who-we-are/brand-toolkit

I further scaled them to match existing assets with Inkscape.

https://x.com/cb_doge/status/1792539920562782254

Also replaced Twitter in links and in post href "tweet" is replaced by "post".

[marknoble]

Addresses # https://github.com/firstcontributions/firstcontributions.github.io/issues/403

Could someone please review?

[marknoble]

@Roshanjossey @Mandy-cyber Could I please get a review on this PR?