Add tests for routing service and node profile serialization

Route calculation to alprwatch API fails with HTTP 400 because
built-in profiles include empty tag values (e.g. camera:mount: '')
that get serialized into the request body and rejected by the API.

Add routing_service_test.dart with 5 tests:
- Empty tags filtered from request (reproduces the bug)
- Successful route parsing
- HTTP error handling
- Network error wrapping
- API-level error surfacing

Add node_profile_test.dart with 4 tests:
- toJson/fromJson round-trip
- getDefaults returns expected profiles
- Empty tag values exist in defaults (documents bug origin)
- Equality based on id

Tests require RoutingService to accept an injectable http.Client,
which will be added in the next commit along with the fix.

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

test/models/node_profile_test.dart

@@ -0,0 +1,76 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:deflockapp/models/node_profile.dart';
+
+void main() {
+  group('NodeProfile', () {
+    test('toJson/fromJson round-trip preserves all fields', () {
+      final profile = NodeProfile(
+        id: 'test-id',
+        name: 'Test Profile',
+        tags: const {'man_made': 'surveillance', 'camera:type': 'fixed'},
+        builtin: true,
+        requiresDirection: false,
+        submittable: true,
+        editable: false,
+        fov: 90.0,
+      );
+
+      final json = profile.toJson();
+      final restored = NodeProfile.fromJson(json);
+
+      expect(restored.id, equals(profile.id));
+      expect(restored.name, equals(profile.name));
+      expect(restored.tags, equals(profile.tags));
+      expect(restored.builtin, equals(profile.builtin));
+      expect(restored.requiresDirection, equals(profile.requiresDirection));
+      expect(restored.submittable, equals(profile.submittable));
+      expect(restored.editable, equals(profile.editable));
+      expect(restored.fov, equals(profile.fov));
+    });
+
+    test('getDefaults returns expected profiles', () {
+      final defaults = NodeProfile.getDefaults();
+
+      expect(defaults.length, greaterThanOrEqualTo(10));
+
+      final ids = defaults.map((p) => p.id).toSet();
+      expect(ids, contains('builtin-flock'));
+      expect(ids, contains('builtin-generic-alpr'));
+      expect(ids, contains('builtin-motorola'));
+      expect(ids, contains('builtin-shotspotter'));
+    });
+
+    test('empty tag values exist in default profiles', () {
+      // Documents that profiles like builtin-flock ship with camera:mount: ''
+      // This is the root cause of the HTTP 400 bug — the routing service must
+      // filter these out before sending to the API.
+      final defaults = NodeProfile.getDefaults();
+      final flock = defaults.firstWhere((p) => p.id == 'builtin-flock');
+
+      expect(flock.tags.containsKey('camera:mount'), isTrue);
+      expect(flock.tags['camera:mount'], equals(''));
+    });
+
+    test('equality is based on id', () {
+      final a = NodeProfile(
+        id: 'same-id',
+        name: 'Profile A',
+        tags: const {'tag': 'a'},
+      );
+      final b = NodeProfile(
+        id: 'same-id',
+        name: 'Profile B',
+        tags: const {'tag': 'b'},
+      );
+      final c = NodeProfile(
+        id: 'different-id',
+        name: 'Profile A',
+        tags: const {'tag': 'a'},
+      );
+
+      expect(a, equals(b));
+      expect(a.hashCode, equals(b.hashCode));
+      expect(a, isNot(equals(c)));
+    });
+  });
+}