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/web/src/pages/repo-workspace.tsx

@@ -196,6 +196,7 @@ export const RepoWorkspace = () => {
               repoId={selectedRepoId}
               currentBranch={currentBranch}
               branches={branches}
+              hasRemote={Boolean(selectedRepo?.remote_url)}
               onBranchChange={(branch) => {
                 setCurrentBranch(branch);
                 const newParams = new URLSearchParams(searchParams);
@@ -391,4 +392,3 @@ const FileBrowser = ({
     </div>
   );
 };
-