test(uddf): make MacDive real-sample suite portable and skip-safe

- Path is now read from MACDIVE_UDDF_SAMPLE (compile-time env var
  set via --dart-define). No more hard-coded developer username.
- Each test checks hasFixture and calls markTestSkipped/return
  if the sample isn't available. --run-skipped --tags=real-data
  now cleanly skips rather than crashing on uninitialized state.
- Added top-of-file comment documenting the env-var workflow.

Addresses Copilot review comments 3 and 4 on PR #252.

Author: ericgriffin

test/core/services/export/uddf/uddf_macdive_real_sample_test.dart

@@ -1,3 +1,16 @@
+/// MacDive real-sample regression suite.
+///
+/// These tests exercise a real MacDive UDDF export that is not checked into
+/// the repository. To run them locally, point the [MACDIVE_UDDF_SAMPLE]
+/// compile-time environment variable at your local sample file:
+///
+///   flutter test \
+///     --dart-define=MACDIVE_UDDF_SAMPLE=/absolute/path/to/sample.uddf \
+///     --run-skipped --tags=real-data \
+///     test/core/services/export/uddf/uddf_macdive_real_sample_test.dart
+///
+/// Without the env var (or when the file at that path does not exist), every
+/// test in this suite is cleanly skipped so CI and fresh clones stay green.
 @Tags(['real-data'])
 library;
 
@@ -6,30 +19,49 @@ import 'dart:io';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:submersion/core/services/export/uddf/uddf_full_import_service.dart';
 
-const _realSamplePath =
-    '/Users/ericgriffin/Documents/submersion development/submersion data/Macdive/Apr 4 no iPad sync.uddf';
+/// Compile-time env var that points at a local MacDive UDDF sample.
+///
+/// Injected via `flutter test --dart-define=MACDIVE_UDDF_SAMPLE=...`.
+const _realSamplePathEnvVar = String.fromEnvironment('MACDIVE_UDDF_SAMPLE');
+
+String? _realSamplePath() {
+  if (_realSamplePathEnvVar.isEmpty) return null;
+  return _realSamplePathEnvVar;
+}
 
 void main() {
   group('MacDive real-sample regression', () {
     late UddfFullImportService service;
     late String content;
+    var hasFixture = false;
 
     setUpAll(() async {
-      final file = File(_realSamplePath);
-      if (!file.existsSync()) {
-        markTestSkipped('Real sample not available in this environment');
-        return;
-      }
+      final path = _realSamplePath();
+      if (path == null) return;
+      final file = File(path);
+      if (!file.existsSync()) return;
       content = await file.readAsString();
       service = UddfFullImportService();
+      hasFixture = true;
     });
 
+    bool skipIfNoFixture() {
+      if (hasFixture) return false;
+      markTestSkipped(
+        'Real sample not available. Set MACDIVE_UDDF_SAMPLE via '
+        '--dart-define and pass --run-skipped --tags=real-data to run.',
+      );
+      return true;
+    }
+
     test('parses 540 dives', () async {
+      if (skipIfNoFixture()) return;
       final result = await service.importAllDataFromUddf(content);
       expect(result.dives.length, 540);
     });
 
     test('every dive has a sourceUuid from <dive id>', () async {
+      if (skipIfNoFixture()) return;
       final result = await service.importAllDataFromUddf(content);
       expect(
         result.dives.every((d) => d['sourceUuid'] is String),
@@ -39,18 +71,21 @@ void main() {
     });
 
     test('parses at least 350 sites', () async {
+      if (skipIfNoFixture()) return;
       final result = await service.importAllDataFromUddf(content);
       expect(result.sites.length, greaterThanOrEqualTo(350));
     });
 
     test('parses at least 30 buddies', () async {
+      if (skipIfNoFixture()) return;
       final result = await service.importAllDataFromUddf(content);
       expect(result.buddies.length, greaterThanOrEqualTo(30));
     });
 
     test(
       'parses at least 20 gear items from <diver><owner><equipment>',
       () async {
+        if (skipIfNoFixture()) return;
         final result = await service.importAllDataFromUddf(content);
         expect(
           result.equipment.length,
@@ -61,6 +96,7 @@ void main() {
     );
 
     test('at least one dive has equipmentRefs populated', () async {
+      if (skipIfNoFixture()) return;
       final result = await service.importAllDataFromUddf(content);
       final withGear = result.dives.where(
         (d) => (d['equipmentRefs'] as List?)?.isNotEmpty ?? false,
@@ -73,6 +109,7 @@ void main() {
     });
 
     test('at least one dive has gas-switch markers', () async {
+      if (skipIfNoFixture()) return;
       final result = await service.importAllDataFromUddf(content);
       final withSwitch = result.dives.where((d) {
         final profile = d['profile'] as List?;
@@ -87,6 +124,7 @@ void main() {
     });
 
     test('at least one site has country populated', () async {
+      if (skipIfNoFixture()) return;
       final result = await service.importAllDataFromUddf(content);
       final withCountry = result.sites.where(
         (s) => (s['country'] as String?)?.isNotEmpty ?? false,