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/BranchPanel.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-  import { Check, ChevronDown, ChevronRight, Folder, FolderOpen, GitBranch, GitMerge, HardDrive, Pencil, Plus, Tag as TagIcon, Trash2, Upload, X } from "@lucide/svelte";
+  import { Check, ChevronDown, ChevronRight, Folder, FolderOpen, GitBranch, GitCompare, GitMerge, HardDrive, Pencil, Plus, Tag as TagIcon, Trash2, Upload, X } from "@lucide/svelte";
   import type { GitBranch as GitBranchInfo, GitTag } from "../types";
 
   type BranchTreeNode = BranchFolderNode | BranchLeafNode;
@@ -49,6 +49,7 @@
     hasRepository: boolean;
     isBusy: boolean;
     onCheckout: (branch: GitBranchInfo) => void;
+    onCompareBranch: (branch: GitBranchInfo) => void;
     onMerge: (branch: GitBranchInfo) => void;
     onRebase: (branch: GitBranchInfo) => void;
     onCreateBranch: (branchName: string) => void | Promise<void>;
@@ -72,6 +73,7 @@
     hasRepository = false,
     isBusy = false,
     onCheckout = () => {},
+    onCompareBranch = () => {},
     onMerge = () => {},
     onRebase = () => {},
     onCreateBranch = () => {},
@@ -250,7 +252,7 @@
     const rawX = rect ? event.clientX - rect.left : event.offsetX;
     const rawY = rect ? event.clientY - rect.top : event.offsetY;
     const maxX = Math.max(8, (rect?.width ?? window.innerWidth) - 192);
-    const maxY = Math.max(8, (rect?.height ?? window.innerHeight) - 190);
+    const maxY = Math.max(8, (rect?.height ?? window.innerHeight) - 226);
 
     contextBranch = branch;
     contextMenuX = Math.max(8, Math.min(rawX, maxX));
@@ -268,6 +270,13 @@
     await onRenameBranch(branch);
   }
 
+  function compareContextBranch() {
+    const branch = contextBranch;
+    if (!branch || isBusy) return;
+    closeBranchContextMenu();
+    onCompareBranch(branch);
+  }
+
   async function deleteContextBranch() {
     const branch = contextBranch;
     if (!branch || branch.current || isBusy) return;
@@ -677,6 +686,10 @@
         <GitBranch size={14} aria-hidden="true" />
         Checkout
       </button>
+      <button type="button" role="menuitem" onclick={compareContextBranch} disabled={isBusy}>
+        <GitCompare size={14} aria-hidden="true" />
+        Compare with...
+      </button>
       <button type="button" role="menuitem" onclick={mergeContextBranch} disabled={isBusy || contextBranch.current}>
         <GitMerge size={14} aria-hidden="true" />
         Merge into current
@@ -690,9 +703,9 @@
         Open in new worktree
       </button>
       <div class="menu-separator" role="separator"></div>
-      <button type="button" role="menuitem" onclick={renameContextBranch} disabled={isBusy || contextBranch.remote}>
+      <button type="button" role="menuitem" onclick={renameContextBranch} disabled={isBusy}>
         <Pencil size={14} aria-hidden="true" />
-        Rename
+        {contextBranch.remote ? "Rename remote..." : "Rename"}
       </button>
       <button
         class="danger"