T19/T21: map and export, completing Phase 4

flutter_map with the same OSM tiles and no-API-key reasoning that chose osmdroid.
All four load-bearing behaviours ported and, unlike the native app's map, tested:
one polyline per segment so a pause is a real gap, render-only decimation, the
zoom clamp at OSM's max tile zoom with a short-ride fallback, and a real user
agent. Speed colouring is bucketed per run rather than per-vertex, since neither
osmdroid nor flutter_map makes per-vertex paint reasonable.

Export via share_plus, which also handles the iPad popover anchor a naive port
forgets. It passes the raw stored points, never the map's decimated path.

164 tests passing, analyze clean.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/src/export/ride_export.dart

@@ -48,7 +48,9 @@ String escapeXml(String text) {
 
 /// Segment order first, then any points whose segment is missing, so nothing is dropped.
 List<int> _orderedSegmentIds(
-    List<Segment> segments, Map<int, List<TrackPoint>> bySegment) {
+  List<Segment> segments,
+  Map<int, List<TrackPoint>> bySegment,
+) {
   final ids = <int>[
     for (final s in segments)
       if (bySegment.containsKey(s.id)) s.id,
@@ -87,7 +89,8 @@ String gpx(
   final b = StringBuffer();
   b.write('<?xml version="1.0" encoding="UTF-8"?>\n');
   b.write(
-      '<gpx version="1.1" creator="Rippr" xmlns="http://www.topografix.com/GPX/1/1">\n');
+    '<gpx version="1.1" creator="Rippr" xmlns="http://www.topografix.com/GPX/1/1">\n',
+  );
   b.write('  <metadata>\n');
   b.write('    <name>${escapeXml(name)}</name>\n');
   b.write('    <time>${_time(trip.startedAt)}</time>\n');
@@ -99,7 +102,8 @@ String gpx(
     b.write('    <trkseg>\n');
     for (final p in bySegment[segmentId]!) {
       b.write(
-          '      <trkpt lat="${_coord(p.latitude)}" lon="${_coord(p.longitude)}">\n');
+        '      <trkpt lat="${_coord(p.latitude)}" lon="${_coord(p.longitude)}">\n',
+      );
       b.write('        <ele>${_num(p.altitudeM)}</ele>\n');
       b.write('        <time>${_time(p.timestamp)}</time>\n');
       b.write('        <extensions>\n');
@@ -129,17 +133,21 @@ String geoJson(
   final bySegment = _groupBySegment(points);
   final ordered = _orderedSegmentIds(segments, bySegment);
 
-  final features = ordered.map((segmentId) {
-    final coords = bySegment[segmentId]!
-        .map((p) =>
-            '[${_coord(p.longitude)}, ${_coord(p.latitude)}, ${_num(p.altitudeM)}]')
-        .join(', ');
-    return '''    {
+  final features = ordered
+      .map((segmentId) {
+        final coords = bySegment[segmentId]!
+            .map(
+              (p) =>
+                  '[${_coord(p.longitude)}, ${_coord(p.latitude)}, ${_num(p.altitudeM)}]',
+            )
+            .join(', ');
+        return '''    {
       "type": "Feature",
       "properties": { "segment_id": $segmentId },
       "geometry": { "type": "LineString", "coordinates": [$coords] }
     }''';
-  }).join(',\n');
+      })
+      .join(',\n');
 
   return '''{
   "type": "FeatureCollection",