fix: use working clones for git repos

- Create normal working clones for remote repositories
- Initialize blank repositories with a main branch
- Align pull and branch helpers with unborn HEAD handling
- Gate fetch/pull on repositories with a remote

Quality gates: vitest repositories-settings-tab (passed); api pytest blocked by missing fastapi in environment

apps/api/src/utils/git_files.py

@@ -346,7 +346,20 @@ def list_branches(repo_path: str) -> tuple[list[BranchInfo], str]:
                 )
                 default_branch = branch_name
         except RuntimeError:
-            pass
+            try:
+                output = _run_git_command(repo_path, "symbolic-ref", "--short", "HEAD")
+                branch_name = output.strip()
+                if branch_name:
+                    branches.append(
+                        BranchInfo(
+                            name=branch_name,
+                            is_default=True,
+                            last_commit=None,
+                        )
+                    )
+                    default_branch = branch_name
+            except RuntimeError:
+                pass
 
     return branches, default_branch