feat(map): reverse geocode location + recenter button on dashboard and history

- Dashboard: recenter button in GPS card header (hidden until first fix)
- Dashboard: estimated location name under lat/lon via Nominatim reverse geocode (throttled 30s)
- History: recenter button fits map back to trip bounds
- Both buttons use crosshairs icon, hidden until data is available

Co-authored-by: Copilot <[email protected]>

static/js/history.js

@@ -21,6 +21,7 @@
     let replayPoints = [];
     let replayTimer = null;
     let replayController = null;
+    const recenterBtn = document.getElementById("btn-recenter-history");
 
     function formatDuration(seconds) {
         const hours = Math.floor(seconds / 3600);
@@ -132,6 +133,14 @@
         } else if (coordinates.length === 1) {
             map.setView(coordinates[0], 15);
         }
+        recenterBtn.hidden = false;
+        recenterBtn.onclick = function () {
+            if (coordinates.length > 1) {
+                map.fitBounds(routeLayer.getBounds(), { padding: [24, 24] });
+            } else if (coordinates.length === 1) {
+                map.setView(coordinates[0], 15);
+            }
+        };
         summary.textContent = `${formatDistance(result.trip.distance_km)} · `
             + `${formatDuration(result.trip.duration_seconds)} · `
             + `avg ${formatSpeed(result.trip.average_speed_kmh)} · `