Fixed: the highlight toolbar didn't appear when selecting text on
Firefox for Android (and other touch browsers). Selecting text via
long-press + drag handles never fires a mouseup/mousedown event, which
is what the toolbar previously relied on exclusively.

• content.js now triggers the toolbar from pointerup (covers mouse,
  pen, and most touch interactions) with a debounced selectionchange
  listener as a fallback for the case where finishing a drag-handle
  selection on Android doesn't fire a pointer event at all.
• The color swatches and the "Remove highlight" button now use
  pointerdown instead of mousedown, so tapping them works the same way
  on touch as clicking does on desktop.

No changes to permissions, storage format, or manifest structure — this is
a drop-in update.