fix(data): force English git output for locale-fragile stderr matches

RevParseHeadAsync and CommitAsync's identity-error detection match
English-only substrings against git stderr. Under a non-English OS/git
locale these silently fail to match, falling through to a generic
error. Force LC_ALL=C and LANGUAGE=C on the git ProcessStartInfo so
git always emits English output regardless of ambient locale.

src/ClaudeDo.Data/Git/GitService.cs

@@ -704,6 +704,11 @@ public sealed class GitService
             // (mktree "input format error") and would prepend to stdin commit messages.
             StandardInputEncoding = stdinData is not null ? new UTF8Encoding(false) : null,
         };
+        // Force English stderr/stdout so the English-only substring matches below
+        // (e.g. "ambiguous argument 'HEAD'", "tell me who you are") work regardless
+        // of the OS locale git for Windows picks up.
+        psi.Environment["LC_ALL"] = "C";
+        psi.Environment["LANGUAGE"] = "C";
         psi.ArgumentList.Add("-C");
         psi.ArgumentList.Add(workDir);
         foreach (var a in args) psi.ArgumentList.Add(a);