add mapbox gl option, gps location, journey reorder + polish

- Mapbox GL provider alongside Leaflet for trip and journey maps (opt-in in
  settings with token, style presets incl. 3D on satellite, quality mode,
  experimental badge).
- GPS "blue dot" with heading cone on mobile; three-state FAB (off / show /
  follow), geodesic accuracy circle, desktop-hidden since browser IP geo is
  too coarse for navigation.
- Marker drift fix: outer wrap no longer carries inline position/transform,
  so mapbox's translate keeps the pin pinned at every zoom and pitch.
- Journey map popup (mapbox-gl): Apple-Maps-style tooltip on marker
  highlight/click showing entry title + location / date subline.
- Journey feed reorder: up/down controls to the left of each entry reorder
  sort_order within a day. Server endpoint, optimistic store update, rollback
  on failure.
- Journey entry editor: desktop modal now centers over the feed column only,
  backdrop still blurs the whole page (map included).
- Scroll-sync guard on journey: marker click locks the sync so smooth-scroll
  can't steer the highlight to a neighbouring entry mid-animation.
- Misc: map top-padding aligned with hero, live/synced badges replaced by a
  compact back-button in the hero, skeleton entries no longer pollute the
  journey map, journey detail no longer shows map on mobile path when
  combined view is active.

client/src/index.css

@@ -6,6 +6,11 @@ html { height: 100%; overflow: hidden; background-color: var(--bg-primary); }
 body { height: 100%; overflow: auto; overscroll-behavior: none; -webkit-overflow-scrolling: touch; }
 
 
+/* Journey desktop feed: hide scrollbar (right column is a sticky map, a
+   visible scrollbar on the left breaks the polarsteps-style reading feel). */
+.journey-feed-scroll { scrollbar-width: none; -ms-overflow-style: none; }
+.journey-feed-scroll::-webkit-scrollbar { display: none; }
+
 /* Leaflet Popups — Enter-Animation vom Anchor-Tip */
 .leaflet-popup {
   animation: trek-popover-enter 220ms cubic-bezier(0.23, 1, 0.32, 1);
@@ -447,6 +452,7 @@ input[type="number"], input[type="time"], input[type="date"], input[type="dateti
   --bg-card: #ffffff;
   --bg-input: #ffffff;
   --bg-hover: rgba(0,0,0,0.03);
+  --bg-selected: #e2e8f0;
   --text-primary: #111827;
   --text-secondary: #374151;
   --text-muted: #6b7280;
@@ -494,6 +500,7 @@ input[type="number"], input[type="time"], input[type="date"], input[type="dateti
   --bg-card: #131316;
   --bg-input: #1c1c21;
   --bg-hover: rgba(255,255,255,0.06);
+  --bg-selected: rgba(255,255,255,0.1);
   --text-primary: #f4f4f5;
   --text-secondary: #d4d4d8;
   --text-muted: #a1a1aa;