Update profile dropdown menu

[ascholerChemeketa]

Adds PTXDropdown framework and uses that to make Profile menu accessible.
Gets rid of hard coded RS menu items.

This builds on #2952

Starting at f46495a

After that PR is in I can rebase to that point.

[rbeezer]

I think this must need a rebase, and I suspect it will be of a bigger magnitude than I should be touching? Along the way, Claude suspects one "dormant" bug and has some nits. Coming next.

[rbeezer]

The PTXDropdown approach is the right move — proper menu semantics and keyboard handling, and it fixes the invalid <div>-inside-<button> nesting the old profile menu had. A few things.

One actual bug:

• In the PTXDropdown constructor, the "close on escape" listener dereferences this.controlElement outside the if (this.controlElement) guard that wraps the other control-element listeners:

  // Close on escape even if opened via click and focus is on button
  this.controlElement.addEventListener("keydown", (event) => {
  if (event.key === "Escape" && this.isOpen()) {

  Since openButton defaults to null and you use this.controlElement?.contains(...) elsewhere, the class is meant to tolerate a null control — so new PTXDropdown(menuEl) would throw here. The current call site passes a button, so it doesn't bite today. Folding this listener into the existing if (this.controlElement) block fixes the crash and also drops a duplicate Escape path (it's already handled in handleKeydown). That inner if is also mis-indented.

Smaller:

• console.log("PTXDropdown: No dropdown element provided.") reads more like a console.warn.
• pretext-dropdown.js has no trailing newline.
• XSL: aria-labelledby="ptx-user-dropdown-button" role="menu" has a double space; and aria-label="Runestone" is the one hardcoded string in the new menu (probably fine as a product name).
• Worth a visual check: the old ptx-dropdown-button mixin set position: relative on the button, and the renamed ptx-dropdown-menu mixin (now on the menu element) uses position: absolute; top: 100%; right: 0 without that anchor — confirm the menu still positions under the button rather than against a higher navbar ancestor.

Claude Opus 4.8, acting as a review assistant for Rob Beezer