Audit casing for breadcrumbs and page titles

Issue

We have a mix of sentence and title casing across page titles and breadcrumbs. What should we be using? 🤔

Proposal

• Title casing for page titles
• Sentence casing for breadcrumbs

The following discussion from !117724 (merged) should be addressed:

• @pgascouvaillancourt started a discussion: (+2 comments)

  nitpick(non-blocking): Apologies for noticing this only now, but it looks like the casing doesn't match the page title. Should it?

  - breadcrumb_title _("Merge Conflicts")

  If we do change this, we'll need to regenerate the translations.