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/CompareDialog.svelte

@@ -20,6 +20,8 @@
     comparison: GitCommitComparison;
     selectedDiffPath: string;
     isBusy: boolean;
+    fromLabel?: string;
+    toLabel?: string;
     restoreLabel?: string;
     /** When opened from a search hit, the term to highlight on matching lines. */
     highlightQuery?: string;
@@ -32,6 +34,8 @@
     comparison,
     selectedDiffPath = "",
     isBusy = false,
+    fromLabel = "",
+    toLabel = "",
     restoreLabel = "",
     highlightQuery = "",
     onClose = () => {},
@@ -219,15 +223,15 @@
   class="dialog-backdrop compare-dialog-backdrop"
   role="presentation"
 >
-  <div class="dialog compare-dialog" role="dialog" aria-modal="true" aria-label="Commit comparison" tabindex="-1">
+  <div class="dialog compare-dialog" role="dialog" aria-modal="true" aria-label="Branch or commit comparison" tabindex="-1">
 
     <header class="dialog-header">
       <div>
         <span class="eyebrow">Compare</span>
         <h2 class="dialog-range">
-          <span class="hash">{comparison.from_short}</span>
+          <span class="hash" title={comparison.from_hash}>{fromLabel || comparison.from_short}</span>
           <ArrowRight size={14} aria-hidden="true" />
-          <span class="hash">{comparison.to_short}</span>
+          <span class="hash" title={comparison.to_hash}>{toLabel || comparison.to_short}</span>
         </h2>
       </div>
       <div class="dialog-header-actions">
@@ -289,11 +293,11 @@
             <div class="split-col-headers">
               <div class="split-col-label">
                 <span>Before</span>
-                <span class="split-col-hash">{comparison.from_short}</span>
+                <span class="split-col-hash" title={comparison.from_hash}>{fromLabel || comparison.from_short}</span>
               </div>
               <div class="split-col-label">
                 <span>After</span>
-                <span class="split-col-hash">{comparison.to_short}</span>
+                <span class="split-col-hash" title={comparison.to_hash}>{toLabel || comparison.to_short}</span>
               </div>
             </div>