feat(ui): New button to favorites sheet and now saving buildings

lib/screens/map_screen.dart

@@ -1841,6 +1841,23 @@ class _MaizeBusCoreState extends State<MaizeBusCore> {
               );
             }
           },
+          onSelectBuilding: (Location location) {
+            _showBuildingSheet(location);
+          },
+          onBuildingGetDirections: (Location location) {
+            Map<String, double>? start;
+            Map<String, double>? end = {
+              'lat': location.latlng!.latitude,
+              'lon': location.latlng!.longitude,
+            };
+            _showDirectionsSheet(
+              start,
+              end,
+              "Current Location",
+              location.name,
+              false,
+            );
+          },
           onUnfavorite: (stpid) {
             // update in memory and marker icons immediately
             setState(() {

lib/util/favorite_building_storage.dart

@@ -0,0 +1,104 @@
+import 'dart:convert';
+
+import 'package:google_maps_flutter/google_maps_flutter.dart';
+
+import '../constants.dart';
+
+const String kFavoriteBuildingsPrefsKey = 'favorite_buildings';
+
+String favoriteBuildingStorageId(Location b) {
+  final ll = b.latlng;
+  if (ll != null) {
+    return 'geo:${ll.latitude.toStringAsFixed(6)},${ll.longitude.toStringAsFixed(6)}';
+  }
+  return 'name:${b.name}';
+}
+
+String encodeFavoriteBuilding(Location b) {
+  final ll = b.latlng;
+  return jsonEncode({
+    'id': favoriteBuildingStorageId(b),
+    'name': b.name,
+    'abbrev': b.abbrev,
+    if (ll != null) 'lat': ll.latitude,
+    if (ll != null) 'lon': ll.longitude,
+  });
+}
+
+/// Stable id for a row in [kFavoriteBuildingsPrefsKey], whether JSON or legacy plain id.
+String? favoriteBuildingEntryId(String stored) {
+  try {
+    final m = jsonDecode(stored) as Map<String, dynamic>;
+    return m['id'] as String?;
+  } catch (_) {
+    if (stored.startsWith('geo:') || stored.startsWith('name:')) {
+      return stored;
+    }
+    return null;
+  }
+}
+
+class FavoriteBuildingEntry {
+  final String raw;
+  final String id;
+  final String name;
+  final String abbrev;
+  final double? lat;
+  final double? lon;
+
+  const FavoriteBuildingEntry({
+    required this.raw,
+    required this.id,
+    required this.name,
+    required this.abbrev,
+    required this.lat,
+    required this.lon,
+  });
+
+  Location? toLocation() {
+    if (lat == null || lon == null) return null;
+    return Location(
+      name,
+      abbrev,
+      const [],
+      false,
+      latlng: LatLng(lat!, lon!),
+    );
+  }
+}
+
+FavoriteBuildingEntry? decodeFavoriteBuildingEntry(String stored) {
+  try {
+    final m = jsonDecode(stored) as Map<String, dynamic>;
+    final id = m['id'] as String?;
+    if (id == null) return null;
+    return FavoriteBuildingEntry(
+      raw: stored,
+      id: id,
+      name: m['name'] as String? ?? 'Building',
+      abbrev: m['abbrev'] as String? ?? '',
+      lat: (m['lat'] as num?)?.toDouble(),
+      lon: (m['lon'] as num?)?.toDouble(),
+    );
+  } catch (_) {
+    return _decodeLegacyFavoriteBuildingEntry(stored);
+  }
+}
+
+FavoriteBuildingEntry? _decodeLegacyFavoriteBuildingEntry(String stored) {
+  if (!stored.startsWith('geo:')) return null;
+  final rest = stored.substring(4);
+  final comma = rest.indexOf(',');
+  if (comma <= 0 || comma >= rest.length - 1) return null;
+  final lat = double.tryParse(rest.substring(0, comma));
+  final lon = double.tryParse(rest.substring(comma + 1));
+  if (lat == null || lon == null) return null;
+  return FavoriteBuildingEntry(
+    raw: stored,
+    id: stored,
+    name: 'Saved building',
+    abbrev: '',
+    lat: lat,
+    lon: lon,
+  );
+}