feat(GRO-2159): drag-to-reorder + re-optimize on route planner

Add @dnd-kit drag-and-drop reorder to the /admin/routes stop list.

- Install @dnd-kit/core, @dnd-kit/sortable, @dnd-kit/utilities
- Sortable stop cards with a grab handle; pointer + touch (press-and-hold)
  + keyboard sensors so mobile groomers and a11y users can reorder
- On drop, PATCH /api/routes/:routeId/reorder { stopOrder } (full order)
- Optimistic UI update with rollback + error message on failure
- Server recomputes legs/buffers/conflicts; response adopted authoritatively
- Tight-schedule conflict warnings retained (server-flagged, gap < travel+buffer)
- "Re-optimize" hint+button after a manual reorder (re-runs POST /optimize)
- Tests: drag handles, conflict flag, no pre-reorder hint, reorder mock
- Updated UAT_PLAYBOOK.md §5.29 — drag-to-reorder & re-optimize cases

Co-Authored-By: Paperclip <noreply@paperclip.ing>

UAT_PLAYBOOK.md

@@ -491,6 +491,20 @@ The admin Route Planner lives at `/admin/routes`. It shows a groomer's geocoded
 | TC-WEB-5.28.7 | Groomer role auto-filter | Sign in as a groomer and open `/admin/routes`. | No groomer selector is shown. The page loads the signed-in groomer's own route for the selected date. The groomer cannot view another groomer's route. |
 | TC-WEB-5.28.8 | Empty / no-route state | Select a date with no appointments. | The map area and stop panel show a friendly empty state ("No stops…"). No crash; **Optimize** is still clickable. |
 
+### 5.29 Route Planner — Drag-to-Reorder & Re-optimize (GRO-2159)
+
+The stop-list panel is drag-sortable (`@dnd-kit`). Each stop card has a grab handle (⠿). Dropping a stop in a new position calls `PATCH /api/routes/:routeId/reorder` with `{ stopOrder: [routeStopId…] }` (full first-to-last order); the UI updates optimistically and rolls back on error. The server recomputes per-leg travel, buffers, totals and tight-schedule conflict flags, and the panel/map/summary adopt the response. A "tight schedule" warning is shown on any stop whose gap is shorter than its travel + buffer. After a manual reorder a hint with a **Re-optimize** button appears (re-runs `POST /api/routes/optimize`). Drag works via mouse (desktop), press-and-hold touch (mobile groomers), and keyboard (focus handle → Space → arrows → Space).
+
+| Test Case | Description | Steps | Expected Result |
+|-----------|-------------|-------|-----------------|
+| TC-WEB-5.29.1 | Drag handle present | Open `/admin/routes` for a route with ≥2 stops. | Each stop card shows a grab handle (⠿) with an accessible label "Drag to reorder <client>". |
+| TC-WEB-5.29.2 | Reorder persists | Drag a stop to a new position and drop it. | A `PATCH /api/routes/:routeId/reorder` fires with the new `stopOrder` (every stop id once, new order). Stop numbers, the map polyline order, and travel-from-previous labels refresh to match. |
+| TC-WEB-5.29.3 | Optimistic update + rollback | Simulate a failing reorder (e.g. server returns an error / offline). | The list shows the new order immediately, then reverts to the prior order when the PATCH fails, and an error message is shown. No stuck/partial order. |
+| TC-WEB-5.29.4 | Tight-schedule warning re-evaluated | Reorder so two stops are too close together. | The affected stop card shows "⚠ Tight schedule — travel + buffer may exceed the gap" (red border) after the server recomputes; warnings clear on a roomier order. |
+| TC-WEB-5.29.5 | Re-optimize button | After a manual drag reorder, locate the hint banner. | A "Stops reordered manually…" hint with a **Re-optimize** button appears. Clicking it fires `POST /api/routes/optimize` and the hint clears once the optimized route loads. The hint is absent before any manual reorder. |
+| TC-WEB-5.29.6 | Touch / mobile drag | On a touch device (or mobile emulation), press-and-hold a stop's handle (~200ms) then drag. | The stop lifts and can be dropped in a new position; page scroll is not hijacked by a quick swipe. Reorder persists as in 5.29.2. |
+| TC-WEB-5.29.7 | Groomer reorders own route | Sign in as a groomer, reorder stops on the own route. | Reorder succeeds (groomer is authorized for their own route). |
+
 ## 6. Pass/Fail Criteria
 
 **Pass:**