feat(frontend): one grip reorder affordance for tags and trigger words

Model tags could already be reordered by dragging a chip, but the only
hint was a `cursor: grab` on `.metadata-item` — a hover-only, mouse-only
signal that also leaked into the bulk add-tags modal, where the chips are
not sortable at all. Trigger words could not be reordered, and their
order matters: "Copy Trigger Words" and the insert-into-node action join
the array as-is to build a prompt.

Both editors now share one vocabulary: a `⠿` grip that appears whenever
the list has something to order, plus `Alt + arrow` keyboard moves with
an aria-live announcement. Whether the chip body is draggable is a
property of the item rather than of the feature:

- tags have no click action of their own, so the whole chip stays
  draggable (`handleSelector: null`), with a 5px threshold so a click on
  the grip only focuses it
- trigger words keep click-to-edit on the body, so a drag starts from the
  grip only
- the grip is the element that opts out of touch scrolling
  (`touch-action: none`), so touch users drag by the grip in both editors
- reordering is offered only while editing: trigger words reveal the grip
  from `.edit-mode`, tags from the edit container, which stays hidden
  outside edit mode

The drag engine moves out of ModelTags.js into shared/pointerSort.js,
which now marks sortable containers with `pointer-sort-enabled` so only
lists that really sort show the grab cursor. Labels, the sortable flag,
the keyboard handler and the live region live in
shared/reorderSupport.js, and both editors render the same three
`common.reorder.*` keys (translations follow in the next commit).

Two inherited engine bugs are fixed on the way: the drop position was
only settled when an animation frame was still pending, so a fast drag
(or one that started by crossing the threshold) fell back into its
original slot; and the guard that stops a drop from triggering the chip's
own click handler was removed on a timer, swallowing unrelated clicks
until the next task.

static/css/components/shared/edit-metadata.css

@@ -92,41 +92,126 @@
   border-radius: var(--border-radius-xs);
   padding: 4px 8px;
   position: relative;
-  cursor: grab;
   transition: transform 0.18s ease;
 }
 
-.metadata-item:active {
+/* --- Shared chip reordering (tags + trigger words) ------------------------ */
+/* Chips in a list that is actually sortable advertise the grab gesture only
+   then, so lists that cannot be reordered never lie about it. */
+
+.metadata-items.pointer-sort-enabled .metadata-item {
+  cursor: grab;
+}
+
+.metadata-items.pointer-sort-enabled .metadata-item:active {
   cursor: grabbing;
 }
 
-.metadata-item-dragging {
+/* Grip handle: always in the DOM, revealed when the list is sortable */
+.reorder-handle {
+  display: none;
+  align-items: center;
+  justify-content: center;
+  flex-shrink: 0;
+  padding: 0;
+  margin-left: -2px;
+  border: none;
+  background: transparent;
+  color: var(--text-color);
+  opacity: 0.4;
+  font-size: 0.8em;
+  line-height: 1;
+  cursor: grab;
+  /* Keep a touch drag on the handle from scrolling the surrounding panel */
+  touch-action: none;
+  transition: opacity 0.2s ease, color 0.2s ease;
+}
+
+.has-sortable-words .reorder-handle {
+  display: inline-flex;
+}
+
+/* Tag chips have no flex gap (unlike trigger word tags), so the grip needs its
+   own spacing before the tag text */
+.metadata-item .reorder-handle {
+  margin-right: 4px;
+}
+
+.reorder-handle:hover,
+.reorder-handle:focus-visible {
+  opacity: 0.9;
+  color: var(--lora-accent);
+}
+
+.reorder-handle:focus-visible {
+  outline: 2px solid var(--lora-accent);
+  outline-offset: 1px;
+  border-radius: 2px;
+}
+
+.reorder-handle:active {
+  cursor: grabbing;
+}
+
+/* Hint shown in the edit controls row while reordering is available */
+.reorder-hint {
+  display: none;
+  align-items: center;
+  gap: 4px;
+  margin-right: auto;
+  font-size: 0.75em;
+  color: var(--text-color);
+  opacity: 0.6;
+  white-space: nowrap;
+}
+
+.has-sortable-words .reorder-hint {
+  display: inline-flex;
+}
+
+/* Snapped-to-grid transition for the remaining chips while dragging */
+.reorder-sorting > * {
+  transition: transform 0.18s ease;
+}
+
+/* The lifted chip that follows the pointer */
+.reorder-dragging {
   box-shadow: var(--shadow-dialog);
   cursor: grabbing;
   opacity: 0.95;
   transition: none;
 }
 
-.metadata-item-placeholder {
+/* Drop target left behind by the lifted chip */
+.reorder-placeholder {
   border: 1px dashed var(--lora-accent);
   border-radius: var(--border-radius-xs);
   background: rgba(255, 255, 255, 0.1);
   pointer-events: none;
 }
 
-.metadata-items-sorting .metadata-item {
-  transition: transform 0.18s ease;
-}
-
-body.metadata-drag-active {
+body.reorder-drag-active {
   user-select: none;
   cursor: grabbing;
 }
 
-body.metadata-drag-active * {
+body.reorder-drag-active * {
   cursor: grabbing !important;
 }
 
+/* Screen-reader-only live region announcing reorder moves */
+.reorder-sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border: 0;
+}
+
 .metadata-item-content {
   color: var(--lora-accent) !important;
   font-size: 0.85em;