fix git.branches: use pipe separator instead of null byte

The null byte in the --format string didn't survive Process.run
argument passing, so the output was unparseable and no branches
were returned. Switched to pipe separator with lastIndexOf split
to handle branch names containing pipes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/src/git/operations.dart

@@ -199,16 +199,18 @@ Future<List<({String name, bool current})>> gitBranches(
     Directory workDir) async {
   final r = await Process.run(
     'git',
-    ['branch', '--format=%(refname:short)\x00%(HEAD)'],
+    ['branch', '--format=%(refname:short)|%(HEAD)'],
     workingDirectory: workDir.path,
   );
   if (r.exitCode != 0) return const [];
   final out = <({String name, bool current})>[];
   for (final line in (r.stdout as String).split('\n')) {
     if (line.trim().isEmpty) continue;
-    final parts = line.split('\x00');
-    if (parts.length < 2) continue;
-    out.add((name: parts[0], current: parts[1].trim() == '*'));
+    final sep = line.lastIndexOf('|');
+    if (sep < 0) continue;
+    final name = line.substring(0, sep);
+    final head = line.substring(sep + 1).trim();
+    out.add((name: name, current: head == '*'));
   }
   return out;
 }