UI-02: animated skeleton map when tiles can't be fetched

Adds MapConnectivityState, a shared tracker of tile-fetch outcomes (cache
miss + network failure) that flips every map into an animated skeleton
after 3 consecutive failures and recovers on a single success -- either an
ordinary fetch succeeding, or (once TileLayer has been fully unmounted in
skeleton mode) a periodic single-tile probe every 15s. Detected at the
fetch level rather than via an OS connectivity API, since a captive portal
or degraded connection can report "online" while every real fetch times
out.

SkeletonMapLayer reuses the Stitch exports' 40px grid-overlay treatment
with a shimmer sweep, replacing TileLayer entirely (never fetching
underneath its own placeholder) while markers/polylines keep rendering
since they come from local data. RideMap and the route planner's
independent FlutterMap both wire this in via a plain skeletonMode bool.

Moved the tile-source constants into a new tiles/tile_config.dart so the
connectivity probe (in the app-layer composition root) doesn't need to
import from ui/ to build its request URL.

Verified end-to-end on a real emulator: cut network, cleared the tile
cache, confirmed the skeleton renders after real fetch failures, then
confirmed automatic recovery within one probe interval once network
returned -- not just via the widget/unit tests that also cover this.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012Xki7YAcc2TiN2PRZJ2tXr

test/ride_map_test.dart

@@ -3,6 +3,7 @@ import 'package:flutter_map/flutter_map.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:rippr/src/domain/models.dart';
 import 'package:rippr/src/ui/components/ride_map.dart';
+import 'package:rippr/src/ui/components/skeleton_map_layer.dart';
 import 'package:rippr/src/ui/theme.dart';
 
 /// Tiles are never fetched here — a widget test cannot serve them — but the polyline
@@ -117,4 +118,67 @@ void main() {
     expect(map.options.maxZoom, maxTileZoom,
         reason: 'exceeding OSM max tile zoom renders an empty grid');
   });
+
+  group('skeleton mode (UI-02)', () {
+    testWidgets('shows the skeleton and no TileLayer when skeletonMode is true',
+        (tester) async {
+      await tester.pumpWidget(MaterialApp(
+        theme: ripprTheme(),
+        home: const Scaffold(
+          body: RideMap(points: [], segments: [], showEmptyLabel: false, skeletonMode: true),
+        ),
+      ));
+      await tester.pump();
+
+      expect(find.byType(SkeletonMapLayer), findsOneWidget);
+      expect(find.byType(TileLayer), findsNothing);
+    });
+
+    testWidgets('shows the TileLayer and no skeleton when skeletonMode is false',
+        (tester) async {
+      await tester.pumpWidget(MaterialApp(
+        theme: ripprTheme(),
+        home: const Scaffold(
+          body: RideMap(points: [], segments: [], showEmptyLabel: false),
+        ),
+      ));
+      await tester.pump();
+
+      expect(find.byType(TileLayer), findsOneWidget);
+      expect(find.byType(SkeletonMapLayer), findsNothing);
+    });
+
+    testWidgets('the recorded path still renders on top of the skeleton',
+        (tester) async {
+      final points = [
+        for (var i = 0; i < 4; i++)
+          TrackPoint(
+            id: i + 1,
+            tripId: 1,
+            segmentId: 1,
+            timestamp: 1000 + i * 1000,
+            latitude: 51.0 + i * 0.0005,
+            longitude: -114.0,
+            speedKmh: 40,
+            altitudeM: 1000,
+          ),
+      ];
+      const segments = [Segment(id: 1, tripId: 1, startedAt: 0, endedAt: 1)];
+
+      await tester.pumpWidget(MaterialApp(
+        theme: ripprTheme(),
+        home: Scaffold(
+          body: RideMap(points: points, segments: segments, skeletonMode: true),
+        ),
+      ));
+      await tester.pump();
+
+      expect(find.byType(SkeletonMapLayer), findsOneWidget);
+      expect(find.byType(TileLayer), findsNothing);
+      final layer = tester.widget<PolylineLayer>(find.byType(PolylineLayer));
+      expect(layer.polylines, isNotEmpty,
+          reason: 'the path comes from local data, not tiles -- it must not vanish '
+              'just because the tile fetch is failing');
+    });
+  });
 }