Add drag & drop reordering of trips on the dashboard

- trip_members.sort_order (per-user, migrated) drives GET /api/trips order
- PATCH /api/trips/:id/order updates only the caller's membership row
- Trip cards get a drag handle reusing the generalized row-reorder helper;
  clicking the card still navigates

public/js/views/trips.js

@@ -2,6 +2,7 @@
 import { api } from '../api.js';
 import { el, mount, clear, loading, errorBox, emptyState, toast } from '../dom.js';
 import { formatRange, ymd, parseYMD, pluralize, normalizeCode } from '../format.js';
+import { enableTripReorder } from './dragdrop.js';
 
 export function renderTrips(container, ctx) {
   mount(container, loading('Loading your trips…'));
@@ -57,27 +58,46 @@ export function renderTrips(container, ctx) {
       );
     } else {
       const grid = el('div', { class: 'trip-grid' });
-      for (const trip of trips) grid.appendChild(tripCard(trip));
+      // Reordering only makes sense with 2+ trips (mirrors the day editor's
+      // entry-row reorder — see dragdrop.js).
+      const reorderable = trips.length > 1;
+      const rows = [];
+      for (const trip of trips) {
+        const { node, handle } = tripCard(trip, reorderable);
+        if (reorderable) rows.push({ node, handle, trip });
+        grid.appendChild(node);
+      }
       page.appendChild(grid);
+      if (reorderable) enableTripReorder(rows, load);
     }
 
     mount(container, page);
   }
 
-  function tripCard(trip) {
+  function tripCard(trip, reorderable) {
     const today = ymd(new Date());
     const future = trip.start_date > today;
     const daysUntil = future
       ? Math.round((parseYMD(trip.start_date) - parseYMD(today)) / 86400000)
       : 0;
-    return el(
+    const handle = reorderable
+      ? el('span', {
+          class: 'trip-drag-handle',
+          title: 'Drag to reorder',
+          'aria-hidden': 'true',
+          onClick: (e) => e.preventDefault(),
+        }, '⋮⋮')
+      : null;
+    const node = el(
       'a',
-      { class: 'trip-card card', href: `#/trip/${trip.id}` },
+      { class: 'trip-card card', href: `#/trip/${trip.id}`, draggable: 'false' },
       el(
         'div',
         { class: 'trip-card-top' },
         el('h3', { class: 'trip-card-name' }, trip.name),
-        el('span', { class: `role-badge role-${trip.role}` }, trip.role),
+        el('div', { class: 'trip-card-top-right' },
+          handle,
+          el('span', { class: `role-badge role-${trip.role}` }, trip.role)),
       ),
       el(
         'div',
@@ -93,6 +113,7 @@ export function renderTrips(container, ctx) {
         el('span', { class: 'trip-card-currency' }, trip.currency || 'USD'),
       ),
     );
+    return { node, handle };
   }
 
   // Render `build()` into the slot, or close it if the same panel is open.