Delegate network tile fetching to NetworkTileProvider

Replace our custom tile pipeline (fetchRemoteTile / _SimpleSemaphore /
exponential backoff) with flutter_map's built-in NetworkTileProvider,
gaining persistent disk cache, ETag revalidation, RetryClient, and
obsolete request aborting for free.

DeflockTileProvider now extends NetworkTileProvider and overrides
getTileUrl() to route through TileType.getTileUrl() (quadkey,
subdomains, API keys). getImageWithCancelLoadingSupport() routes
between two paths at runtime: the common network path (super) when
no offline areas exist, and a DeflockOfflineTileImageProvider for
offline-first when they do.

- Delete tiles_from_remote.dart (semaphore, retry loop, spatial helpers)
- Simplify MapDataProvider._fetchRemoteTileFromCurrentProvider to plain
  http.get (only used by offline area downloader now)
- Remove dead clearTileQueue/clearTileQueueSelective from MapDataProvider
- Remove 7 tile fetch constants from dev_config.dart
- TileLayerManager now disposes provider on cache clear and uses actual
  urlTemplate for cache key generation
- 9 new tests covering URL delegation, routing, and equality

Closes #87 Phase 2.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/widgets/map/tile_layer_manager.dart

@@ -22,7 +22,7 @@ class TileLayerManager {
 
   /// Dispose of resources
   void dispose() {
-    // No resources to dispose with the new tile provider
+    _tileProvider?.dispose();
   }
 
   /// Check if cache should be cleared and increment rebuild key if needed.
@@ -45,7 +45,8 @@ class TileLayerManager {
     if (shouldClear) {
       // Force map rebuild with new key to bust flutter_map cache
       _mapRebuildKey++;
-      // Also force new tile provider instance to ensure fresh cache
+      // Dispose old provider before creating a fresh one (closes HTTP client)
+      _tileProvider?.dispose();
       _tileProvider = null;
       debugPrint('[TileLayerManager] *** CACHE CLEAR *** $reason changed - rebuilding map $_mapRebuildKey');
     }
@@ -58,7 +59,7 @@ class TileLayerManager {
 
   /// Clear the tile request queue (call after cache clear)
   void clearTileQueue() {
-    // With the new tile provider, clearing is handled by FlutterMap's internal cache
+    // With NetworkTileProvider, clearing is handled by FlutterMap's internal cache
     // We just need to increment the rebuild key to bust the cache
     _mapRebuildKey++;
     debugPrint('[TileLayerManager] Cache cleared - rebuilding map $_mapRebuildKey');
@@ -66,14 +67,12 @@ class TileLayerManager {
 
   /// Clear tile queue immediately (for zoom changes, etc.)
   void clearTileQueueImmediate() {
-    // No immediate clearing needed with the new architecture
-    // FlutterMap handles this naturally
+    // No immediate clearing needed — NetworkTileProvider aborts obsolete requests
   }
-  
+
   /// Clear only tiles that are no longer visible in the current bounds
   void clearStaleRequests({required LatLngBounds currentBounds}) {
-    // No selective clearing needed with the new architecture  
-    // FlutterMap's internal caching is efficient enough
+    // No selective clearing needed — NetworkTileProvider aborts obsolete requests
   }
 
   /// Build tile layer widget with current provider and type.
@@ -84,16 +83,18 @@ class TileLayerManager {
   }) {
     // Create a fresh tile provider instance if we don't have one or cache was cleared
     _tileProvider ??= DeflockTileProvider();
-    
-    // Use provider/type info in URL template for FlutterMap's cache key generation
-    // This ensures different providers/types get different cache keys
-    final urlTemplate = '${selectedProvider?.id ?? 'unknown'}/${selectedTileType?.id ?? 'unknown'}/{z}/{x}/{y}';
-    
+
+    // Use the actual urlTemplate from the selected tile type. Our getTileUrl()
+    // override handles the real URL generation; flutter_map uses urlTemplate
+    // internally for cache key generation.
+    final urlTemplate = selectedTileType?.urlTemplate
+        ?? '${selectedProvider?.id ?? 'unknown'}/${selectedTileType?.id ?? 'unknown'}/{z}/{x}/{y}';
+
     return TileLayer(
-      urlTemplate: urlTemplate, // Critical for cache key generation
+      urlTemplate: urlTemplate,
       userAgentPackageName: 'me.deflock.deflockapp',
       maxZoom: selectedTileType?.maxZoom.toDouble() ?? 18.0,
       tileProvider: _tileProvider!,
     );
   }
-}
+}