feat(git): rename remote branches atomically via push

Adds a new command to rename remote branches and update tracking refs.
Renaming remote refs is performed atomically using a single push.
The push creates the new remote ref and deletes the old if it succeeds.
The frontend now invokes remote-rename when needed and shows labels.

- Atomic remote rename via push with create/ref and delete
- Frontend supports remote branch renames from the branch panel
- Compare UI now shows labels for remote refs in results

src/lib/components/CommandPalette.svelte

@@ -47,7 +47,7 @@
     action("push", "push", "Push", isGerman ? "Lokale Commits veröffentlichen" : "Publish local commits", onPush),
     action("refresh", "refresh", isGerman ? "Repository aktualisieren" : "Refresh repository", isGerman ? "Status und Historie neu laden" : "Reload status and history", onRefresh),
     action("search", "search", isGerman ? "Globale Codesuche" : "Global code search", isGerman ? "Code und Dateihistorie durchsuchen" : "Search code and file history", onOpenSearch),
-    action("compare", "compare", isGerman ? "Commits vergleichen" : "Compare commits", isGerman ? "Unterschiede zwischen zwei Revisionen" : "Diff two revisions", onOpenCompare),
+    action("compare", "compare", isGerman ? "Branches oder Commits vergleichen" : "Compare branches or commits", isGerman ? "Zwei vollständige Revisionen vergleichen" : "Diff two complete revisions", onOpenCompare),
     action("reflog", "reflog", "Reflog", isGerman ? "Verlorene Commits finden und wiederherstellen" : "Find and recover lost commits", onOpenReflog),
     action("rebase", "rebase", "Interactive Rebase", isGerman ? "Commit-Historie bearbeiten" : "Edit commit history", onOpenInteractiveRebase),
     action("worktrees", "worktrees", "Worktrees", isGerman ? "Arbeitsverzeichnisse verwalten" : "Manage linked working trees", onOpenWorktrees),