Metadata: Make title and description default and don't repeat it

[andygrunwald]

I feel (no check with data to back it up) we copy and paste the title and description in https://github.com/EngineeringKiosk/webpage/blob/main/src/pages/linktree.astro#L7-L8

Lets centralize them or make it the default in the Header component, if no title/description is given.

[woolfg]

or even better, change it to represent the content. in general description is just for SEO. maybe we should exclude linktree from the sitemap as it is not really relevant for search engines?