Make stay bands draggable to move stays between days

Dragging any week-segment of a stay band onto an in-range day moves the
whole stay there, preserving its length (same one-PATCH date+end_date
shift the multi-day chips use). Clicking a band still opens the editor.

public/js/views/stayBands.js

@@ -4,6 +4,7 @@
 // partitioning) so a stay keeps the same vertical position across weeks.
 import { el } from '../dom.js';
 import { parseYMD, daysBetweenInclusive, typeInfo, stayShortName, entrySpanDays } from '../format.js';
+import { makeBandDraggable } from './dragdrop.js';
 
 // Per-instance band palette: each stay gets its own hue (not the generic stay
 // type colour) so overlapping/adjacent areas read apart. Muted-but-distinct
@@ -97,6 +98,9 @@ export function renderWeekBands(weekYmd, layout, tctx) {
     band.addEventListener('keydown', (e) => {
       if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); open(e); }
     });
+    // Standard HTML5 DnD doesn't fire click after a real drag, so a plain
+    // click still opens the day editor with no extra guard needed.
+    makeBandDraggable(band, s.entry);
     strip.appendChild(band);
   }
   return strip;