fix(claude-do): merge Modify/Delete- und Rename-Konflikte im Merge sichtbar machen

ClaudeDo-Task: 059bcf98-34d5-4ca0-822d-317980fadf8d

src/ClaudeDo.Data/Git/GitService.cs

@@ -376,6 +376,32 @@ public sealed class GitService
             throw new InvalidOperationException($"git add '{path}' failed (exit {exitCode}): {stderr}");
     }
 
+    /// <summary>
+    /// Stages <paramref name="path"/> as deleted (`git rm -f`), removing it from both the index
+    /// and, if present, the working tree. Used to resolve a merge conflict to "keep the
+    /// deletion" — unlike <see cref="AddPathAsync"/>, which would stage an empty file as a
+    /// tracked, zero-byte file rather than actually removing it.
+    /// </summary>
+    public async Task RemovePathAsync(string repoDir, string path, CancellationToken ct = default)
+    {
+        var (exitCode, _, stderr) = await RunGitAsync(repoDir, ["rm", "-f", "--", path], ct);
+        if (exitCode != 0)
+            throw new InvalidOperationException($"git rm '{path}' failed (exit {exitCode}): {stderr}");
+    }
+
+    /// <summary>
+    /// Content of <paramref name="path"/> at a merge stage (1=base, 2=ours, 3=theirs) via
+    /// `git show :&lt;stage&gt;:&lt;path&gt;`. Null when that stage doesn't exist for the path —
+    /// the conventional way to tell a modify/delete or rename/delete conflict apart from an
+    /// ordinary content conflict (git never writes `&lt;&lt;&lt;&lt;&lt;&lt;&lt;` markers for those,
+    /// it just leaves whichever side wasn't deleted in the working tree).
+    /// </summary>
+    public async Task<string?> ShowConflictStageAsync(string repoDir, int stage, string path, CancellationToken ct = default)
+    {
+        var (exitCode, stdout, _) = await RunGitAsync(repoDir, ["show", $":{stage}:{path}"], ct, trimOutput: false);
+        return exitCode == 0 ? stdout : null;
+    }
+
     /// <summary>
     /// Non-destructive mergeability probe via `git merge-tree --write-tree`. Writes only
     /// loose objects — the working tree, index, and refs are left untouched.