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/BranchPanel.svelte

@@ -49,6 +49,7 @@
     isBusy: boolean;
     onCheckout: (branch: GitBranchInfo) => void;
     onMerge: (branch: GitBranchInfo) => void;
+    onRebase: (branch: GitBranchInfo) => void;
     onCreateBranch: (branchName: string) => void | Promise<void>;
     onRenameBranch: (branch: GitBranchInfo) => void | Promise<void>;
     onDeleteBranch: (branch: GitBranchInfo) => void | Promise<void>;
@@ -62,6 +63,7 @@
     isBusy = false,
     onCheckout = () => {},
     onMerge = () => {},
+    onRebase = () => {},
     onCreateBranch = () => {},
     onRenameBranch = () => {},
     onDeleteBranch = () => {},
@@ -370,6 +372,10 @@
                         <GitMerge size={15} aria-hidden="true" />
                         Merge
                       </button>
+                      <button class="btn-sm" type="button" onclick={() => onRebase(row.branch)} disabled={isBusy} title="Rebase current branch onto this branch">
+                        <GitBranch size={15} aria-hidden="true" />
+                        Rebase
+                      </button>
                     </div>
                   {/if}
                 </article>
@@ -446,6 +452,10 @@
                         <GitMerge size={15} aria-hidden="true" />
                         Merge
                       </button>
+                      <button class="btn-sm" type="button" onclick={() => onRebase(row.branch)} disabled={isBusy} title="Rebase current branch onto this branch">
+                        <GitBranch size={15} aria-hidden="true" />
+                        Rebase
+                      </button>
                     </div>
                   {/if}
                 </article>