feat: A11y fixes - #2148

- Add aria-label to icon-only ActionIcon triggers across tree, comments,
  share, group, breadcrumbs, templates, AI chat, API keys, and spaces
- Give custom clickable divs/spans (color swatches, status swatches,
  load-more, PDF error, comment selection) role="button", tabIndex,
  and keyboard handlers
- Add listbox/combobox semantics (role, aria-selected, aria-activedescendant)
  to slash menu, emoji menu, mention list, and link editor results
- Add aria-haspopup/aria-expanded to bubble-menu triggers (node, text
  align, color) and status badge
- Add aria-label to Modal.Root/Dialog instances that lack a title prop
  (page history, template preview, trash preview, drawio, comment,
  find-and-replace, page verification)
- Add en-US translations for new aria-label strings