feat(git): add rebase workflow with UI state handling

This introduces Git rebase commands (start, continue, abort) and
exposes whether a rebase is currently in progress via the status
payload. The UI now blocks committing during an active rebase and
shows a dedicated rebase notice with continue/abort actions.

- Add tauri commands for rebase operations and status detection
- Update frontend to render rebase state and controls
- Adjust conflict/resolution messaging and related UI styling

src/lib/components/ResolveDialog.svelte

@@ -261,13 +261,13 @@
     style="grid-template-rows: auto minmax(0,1fr) auto;"
     role="dialog"
     aria-modal="true"
-    aria-label="Resolve merge conflicts"
+    aria-label="Resolve conflicts"
     tabindex="-1"
   >
     <header class="dialog-header">
       <div>
         <span class="eyebrow">Resolve</span>
-        <h2 class="dialog-title">Merge conflicts</h2>
+        <h2 class="dialog-title">Conflicts</h2>
       </div>
       <button class="dialog-close" type="button" onclick={onClose} title="Close">
         <X size={18} aria-hidden="true" />
@@ -275,7 +275,7 @@
     </header>
 
     {#if conflictedFiles.length === 0}
-      <div class="blank-state">All conflicts resolved. You can commit the merge now.</div>
+      <div class="blank-state">All conflicts resolved. Continue the current operation when ready.</div>
     {:else}
       <div class="dialog-body">
         <aside class="dialog-files" aria-label="Conflicted files">