Normalize trailing slashes in PRIMARY_SITE_URL

[maxfenton]

• adds a config/general.php alias for @primarySiteUrl that always has a trailing slash
• updates the default Site to use the alias
• updates config/vite.php to remove that trailing slash

[joshuapease]

Would you be able to put this file in a separate PR?

We'll also need to update composer-scripts/post-create-project.php to change that PRIMARY_SITE_URL

I'm happy to make that change, or feel free to go for it if you have time.

If you hit any snags testing it out, I'm happy to pair up later this week or early tomorrow.

[maxfenton]

I've removed the extra changes and force-pushed. I don't really understand about the post-create-project.php file

[joshuapease]

It's a little funky. We should just finally do our Craft modules 1:1 and maybe piggy back some site starter stuff while we're doing it.