Summary: Several Phorge pages include `<h1>` and `<h3>` HTML elements but no `<h2>` elements. * https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/Heading_Elements instructs to "nest headings without skipping levels"; see also its "Don't do this" section. * https://www.w3.org/WAI/tutorials/page-structure/headings/ says that "Skipping heading ranks can be confusing and should be avoided where possible: Make sure that a <h2> is not followed directly by an <h4>, for example." Closes T16124 Test Plan: * Look at the HTML source of a Maniphest task, a Paste, a Differential change, a Diffusion commit. See that h3 elements are replaced by h2 elements. * Look at http://phorge.localhost/phame/ which used h2 elements before, no change. * Optionally, run an Accessibility check in Chromium Lighthouse. Reviewers: O1 Blessed Committers, mainframe98 Reviewed By: O1 Blessed Committers, mainframe98 Subscribers: mainframe98, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno Maniphest Tasks: T16124 Differential Revision: https://we.phorge.it/D26115