m4: drag-to-reorder polish — grip handle + drop affordances

Refine the masonry drag interaction (task 1869) so reordering reads as
intentional instead of an accidental, feedbackless jump:

- explicit grip handle (top-left, hover-revealed, board views only) gates
  dragging — a plain click or text-select no longer starts a drag
- source card dims while dragging; the card under the pointer shows a
  brand ring + slight lift, so the drop position is clear before release
- proper move cursor via dataTransfer effectAllowed/dropEffect
- dragleave uses a relatedTarget guard so the target ring doesn't flicker
  over child elements
- clear drag state on dragend (BoardView clears the tracked source even
  when a drag is cancelled off-target)
- add a "grip" icon to the shared Icon set

Native HTML5 DnD stays library-free; it remains a desktop/mouse
affordance (touch reorder is the M5 Android client's domain).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/components/Icon.vue

@@ -18,6 +18,7 @@ const paths: Record<string, string> = {
   image: '<rect width="18" height="18" x="3" y="3" rx="2"/><circle cx="9" cy="9" r="2"/><path d="m21 15-3.086-3.086a2 2 0 0 0-2.828 0L6 21"/>',
   graph: '<circle cx="18" cy="5" r="3"/><circle cx="6" cy="12" r="3"/><circle cx="18" cy="19" r="3"/><line x1="8.59" x2="15.42" y1="13.51" y2="17.49"/><line x1="15.41" x2="8.59" y1="6.51" y2="10.49"/>',
   bell: '<path d="M10.268 21a2 2 0 0 0 3.464 0"/><path d="M3.262 15.326A1 1 0 0 0 4 17h16a1 1 0 0 0 .74-1.673C19.41 13.956 18 12.499 18 8A6 6 0 0 0 6 8c0 4.499-1.411 5.956-2.738 7.326"/>',
+  grip: '<circle cx="9" cy="5" r="1" fill="currentColor"/><circle cx="9" cy="12" r="1" fill="currentColor"/><circle cx="9" cy="19" r="1" fill="currentColor"/><circle cx="15" cy="5" r="1" fill="currentColor"/><circle cx="15" cy="12" r="1" fill="currentColor"/><circle cx="15" cy="19" r="1" fill="currentColor"/>',
 };
 </script>
 

frontend/src/components/NoteCard.vue

@@ -19,12 +19,52 @@ const props = defineProps<{ note: Note; reorderable?: boolean; active?: boolean
 const emit = defineEmits<{
   (e: "open", note: Note): void;
   (e: "dragstart", note: Note): void;
+  (e: "dragend", note: Note): void;
   (e: "drop", note: Note): void;
 }>();
 const notes = useNotesStore();
 
-// When this card becomes the keyboard-focused card, scroll it into view.
 const root = ref<HTMLElement | null>(null);
+
+// --- Drag-to-reorder. Native HTML5 DnD, gated behind an explicit grip handle so
+// a plain click/select never starts a drag by accident. `dragging` dims the
+// source card; `dragOver` shows where the drop will land. ---
+const canDrag = () => !!props.reorderable && !props.note.trashed;
+const grabbing = ref(false); // handle pressed → the card is momentarily draggable
+const dragging = ref(false); // this card is the one being dragged
+const dragOver = ref(false); // another card is hovering over this one as a drop target
+
+function onDragStart(e: DragEvent) {
+  dragging.value = true;
+  if (e.dataTransfer) {
+    e.dataTransfer.effectAllowed = "move";
+    e.dataTransfer.setData("text/plain", props.note.id); // some browsers need a payload to drag
+  }
+  emit("dragstart", props.note);
+}
+function onDragEnd() {
+  dragging.value = false;
+  grabbing.value = false;
+  dragOver.value = false;
+  emit("dragend", props.note);
+}
+function onDragOver(e: DragEvent) {
+  e.preventDefault(); // allow drop
+  if (e.dataTransfer) e.dataTransfer.dropEffect = "move";
+  if (!dragging.value) dragOver.value = true; // don't flag the source as its own target
+}
+function onDragLeave(e: DragEvent) {
+  // dragleave also fires when moving onto a child; only clear when truly leaving the card.
+  const to = e.relatedTarget as Node | null;
+  if (to && root.value?.contains(to)) return;
+  dragOver.value = false;
+}
+function onDrop() {
+  dragOver.value = false;
+  emit("drop", props.note);
+}
+
+// When this card becomes the keyboard-focused card, scroll it into view.
 watch(
   () => props.active,
   (a) => {
@@ -67,12 +107,37 @@ onBeforeUnmount(() => document.removeEventListener("mousedown", onDocMousedown))
   <div
     ref="root"
     class="group relative mb-4 break-inside-avoid rounded-xl border p-3 shadow-sm transition hover:shadow-md"
-    :class="[cardClass(note.color), active ? 'ring-2 ring-brand' : '']"
-    :draggable="reorderable && !note.trashed"
-    @dragstart="emit('dragstart', note)"
-    @dragover.prevent
-    @drop="emit('drop', note)"
+    :class="[
+      cardClass(note.color),
+      dragging ? 'opacity-40' : '',
+      dragOver
+        ? 'scale-[1.02] shadow-lg ring-2 ring-brand ring-offset-2 ring-offset-white dark:ring-offset-neutral-950'
+        : '',
+      active ? 'ring-2 ring-brand' : '',
+    ]"
+    :draggable="canDrag() && grabbing"
+    @dragstart="onDragStart"
+    @dragend="onDragEnd"
+    @dragover="onDragOver"
+    @dragleave="onDragLeave"
+    @drop="onDrop"
   >
+    <!-- Drag handle: reorder is gated behind this grip so a normal click/select
+         never starts a drag. Appears on hover; board views only (reorderable).
+         Mouse-only affordance — native DnD has no keyboard equivalent. -->
+    <button
+      v-if="canDrag()"
+      type="button"
+      tabindex="-1"
+      class="pointer-events-none absolute left-1.5 top-1.5 z-10 flex cursor-grab items-center rounded-full bg-white/85 p-1 text-neutral-500 opacity-0 shadow-sm ring-1 ring-black/5 backdrop-blur-sm transition hover:text-neutral-800 active:cursor-grabbing group-hover:pointer-events-auto group-hover:opacity-100 dark:bg-neutral-900/85 dark:text-neutral-400 dark:ring-white/10 dark:hover:text-neutral-100"
+      title="Drag to reorder"
+      aria-label="Drag to reorder"
+      @mousedown="grabbing = true"
+      @mouseup="grabbing = false"
+    >
+      <Icon name="grip" />
+    </button>
+
     <img
       v-if="note.attachments.length"
       :src="note.attachments[0].url"