feat: search, multi-stop routing, and route display

Full navigation UI with:
- Search bar with 150ms debounced autocomplete from /api/geocode
- Keyboard navigation (arrow keys, Enter, Escape)
- Exact match badge for verified address results
- Multi-stop list with drag-to-reorder (dnd-kit)
- 10-stop cap with disabled state
- Mode selector (drive/walk/bike)
- Valhalla route display with per-leg color polyline
- Maneuver list with instructions, distance, time remaining
- Click maneuver to fly map to that point
- Optimize stops button (3+ stops, uses /optimized_route)
- Responsive: side panel (desktop ≥768px), bottom sheet (mobile)
- Stop pins: green origin, red destination, blue intermediate
- Pin popup with remove button
- Geolocation permission requested on first route, not on load
- Error handling for unroutable pairs
- nginx proxy for /api/ and /valhalla/ endpoints

Dependencies added: zustand, @dnd-kit/core, @dnd-kit/sortable,
@dnd-kit/utilities

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/index.css

@@ -4,4 +4,48 @@ html, body, #root {
   margin: 0;
   padding: 0;
   height: 100%;
+  overflow: hidden;
+}
+
+/* MapLibre popup styling to match dark theme */
+.maplibregl-popup-content {
+  background: #1f2937 !important;
+  border: 1px solid #374151 !important;
+  border-radius: 8px !important;
+  padding: 8px 12px !important;
+  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.5) !important;
+}
+
+.maplibregl-popup-tip {
+  border-top-color: #1f2937 !important;
+  border-bottom-color: #1f2937 !important;
+}
+
+.maplibregl-popup-close-button {
+  color: #9ca3af !important;
+  font-size: 16px !important;
+  padding: 2px 6px !important;
+}
+
+.maplibregl-popup-close-button:hover {
+  color: #fff !important;
+  background: transparent !important;
+}
+
+/* Custom scrollbar for panels */
+::-webkit-scrollbar {
+  width: 6px;
+}
+
+::-webkit-scrollbar-track {
+  background: transparent;
+}
+
+::-webkit-scrollbar-thumb {
+  background: #4b5563;
+  border-radius: 3px;
+}
+
+::-webkit-scrollbar-thumb:hover {
+  background: #6b7280;
 }