feat(git): add ListLocalBranchesAsync

src/ClaudeDo.Data/Git/GitService.cs

@@ -160,6 +160,19 @@ public sealed class GitService
         return stdout.Trim();
     }
 
+    public async Task<List<string>> ListLocalBranchesAsync(string repoDir, CancellationToken ct = default)
+    {
+        var (exitCode, stdout, stderr) = await RunGitAsync(repoDir,
+            ["branch", "--format=%(refname:short)"], ct);
+        if (exitCode != 0)
+            throw new InvalidOperationException($"git branch --format failed (exit {exitCode}): {stderr}");
+
+        return stdout
+            .Split('\n', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
+            .Where(s => s.Length > 0)
+            .ToList();
+    }
+
     public async Task MergeFfOnlyAsync(string repoDir, string branchName, CancellationToken ct = default)
     {
         var (exitCode, _, stderr) = await RunGitAsync(repoDir, ["merge", "--ff-only", branchName], ct);