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/app/providers.dart

@@ -49,8 +49,9 @@ final recordingEngineProvider = Provider<RecordingEngine>((ref) {
 });
 
 /// The live speedo feed, published from the fix callback at GPS rate.
-final liveTelemetryProvider =
-    Provider<LiveTelemetry>((ref) => LiveTelemetry.instance);
+final liveTelemetryProvider = Provider<LiveTelemetry>(
+  (ref) => LiveTelemetry.instance,
+);
 
 // --- Reactive state ---------------------------------------------------------
 
@@ -70,3 +71,9 @@ final recorderStateProvider = StreamProvider<RecorderState>((ref) {
   final engine = ref.watch(recordingEngineProvider);
   return engine.stateStream;
 });
+
+/// Whether the trip-detail map renders.
+///
+/// Kept as a toggle from v2: the map must only ever be live on a visible screen, and no
+/// tile is fetched while recording in the background.
+final mapEnabledProvider = StateProvider<bool>((ref) => true);