URL slugs, edits, and uniqueness

[tzarebczan]

I updated a title for a post, and I was on the old URL, and then refreshed, and that no longer works. Not sure if we want urls to change (at least not automatically from a title rename as because we do have that URL in publication options too) because of renaming - maybe need to make that clearer if someone is editing, or setup redirects automatically (track change?).

This also probably means we need to track all post titles when someone creates a new one, to make sure they don't match others someone has.

[bhavyagor12]

Right now, we have a useEffect that automatically updates the URL whenever the title changes. That logic should be removed.

Instead, the initial URL should be generated once from the title at creation time. After that, any edits to the title must not affect the URL unless the user explicitly changes it via the URL publication setting.

For URL uniqueness, we already validate the URL against all posts within the portal. If a conflict exists, we should block the action and show an alert asking the user to choose a different URL (already in place mostly)