drop hero / inline tab-bar on mobile journey + gallery, eager map tiles

- mobile: journey and gallery views both run as chromeless overlays now.
  The hero card, backlink, stats row and inline tab-bar are hidden; the
  floating top bar (back, Journey/Gallery toggle, settings) handles
  branding for both views, and the gallery content gets a top padding
  that matches the bar so nothing is occluded.
- the journey-title pill below the tab-toggle is removed — the toggle
  itself is enough; the pill just duplicated information.
- JourneyMap tile layer: set updateWhenIdle:false and keepBuffer:4.
  Leaflet defaults to "wait for pan to settle before loading tiles" on
  mobile, which showed as a visible tile-lag when switching timeline
  cards (flyTo moves the map). Eager updates plus a wider off-screen
  ring keep the neighbouring tiles hot.

client/src/components/Journey/JourneyMap.tsx

@@ -183,6 +183,12 @@ const JourneyMap = forwardRef<JourneyMapHandle, Props>(function JourneyMap(
       maxZoom: 18,
       attribution: '&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a>',
       referrerPolicy: 'strict-origin-when-cross-origin',
+      // Leaflet defaults updateWhenIdle:true on mobile (waits for pan to settle
+      // before loading tiles). On the journey mobile combined view we flyTo
+      // constantly when switching cards, so tiles lag visibly — force eager
+      // updates and keep a larger ring of off-screen tiles ready.
+      updateWhenIdle: false,
+      keepBuffer: 4,
     } as any).addTo(map)
 
     const items = buildMarkerItems(entries)