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/telemetry/telemetry.dart

@@ -42,22 +42,21 @@ String formatDuration(int millis) {
 /// boundary. Hoisting them to batch level would silently mislabel points.
 String encodeBatch(String deviceId, List<TrackPoint> points) {
   final array = points
-      .map((p) => <String, Object?>{
-            'id': p.id,
-            'trip_id': p.tripId,
-            'segment_id': p.segmentId,
-            'ts': p.timestamp,
-            'lat': p.latitude,
-            'lon': p.longitude,
-            'speed_kmh': p.speedKmh,
-            'alt_m': p.altitudeM,
-            'acc_m': p.accuracyM,
-            'bearing': p.bearingDeg,
-          })
+      .map(
+        (p) => <String, Object?>{
+          'id': p.id,
+          'trip_id': p.tripId,
+          'segment_id': p.segmentId,
+          'ts': p.timestamp,
+          'lat': p.latitude,
+          'lon': p.longitude,
+          'speed_kmh': p.speedKmh,
+          'alt_m': p.altitudeM,
+          'acc_m': p.accuracyM,
+          'bearing': p.bearingDeg,
+        },
+      )
       .toList(growable: false);
 
-  return jsonEncode(<String, Object?>{
-    'device_id': deviceId,
-    'points': array,
-  });
+  return jsonEncode(<String, Object?>{'device_id': deviceId, 'points': array});
 }