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/app.css

@@ -862,6 +862,8 @@
   .notice.error    { border-color: rgba(232,96,90,0.3); color: #f09090; background: rgba(232,96,90,0.08); }
   .notice.busy     { border-color: rgba(90,140,248,0.28); color: #8ab0f8; background: rgba(90,140,248,0.07); }
   .notice.conflict { border-color: rgba(224,160,64,0.3); color: #e8b060; background: rgba(224,160,64,0.07); }
+  .notice.rebase   { flex-wrap: wrap; border-color: rgba(186,130,255,0.3); color: #c9a8ff; background: rgba(186,130,255,0.075); }
+  .notice.rebase span { min-width: 0; flex: 1 1 auto; }
   .notice.conflict button {
     margin-left: auto;
     min-height: 26px;
@@ -877,6 +879,20 @@
     border-color: rgba(224,160,64,0.45);
     color: #f0c070;
   }
+  .notice.rebase button {
+    min-height: 26px;
+    padding: 0 10px;
+    border-color: rgba(186,130,255,0.28);
+    color: #d5bdff;
+    background: rgba(186,130,255,0.1);
+    font-size: 12px;
+    font-weight: 700;
+  }
+  .notice.rebase button:hover:not(:disabled) {
+    background: rgba(186,130,255,0.18);
+    border-color: rgba(186,130,255,0.45);
+    color: #eadfff;
+  }
 
   /* --- Update toast --- */
 
@@ -1110,6 +1126,10 @@
     gap: 8px;
   }
 
+  .left-sidebar:has(.stash-panel.collapsed) {
+    grid-template-rows: minmax(170px, 0.85fr) auto minmax(220px, 1.15fr);
+  }
+
   /* --- Main panel --- */
 
   .main-panel {
@@ -1276,6 +1296,36 @@
     grid-template-rows: auto auto minmax(0, 1fr);
   }
 
+  .stash-panel.collapsed {
+    grid-template-rows: auto;
+    min-height: 0;
+  }
+
+  .stash-head-actions {
+    display: inline-flex;
+    align-items: center;
+    gap: 6px;
+  }
+
+  .stash-toggle {
+    display: inline-grid;
+    place-items: center;
+    width: 26px;
+    min-width: 26px;
+    min-height: 26px;
+    padding: 0;
+    border-color: rgba(94,110,156,0.18);
+    border-radius: 7px;
+    color: var(--color-ink-dim);
+    background: rgba(255,255,255,0.035);
+  }
+
+  .stash-toggle:hover:not(:disabled) {
+    border-color: rgba(65,209,255,0.28);
+    color: var(--color-ink);
+    background: rgba(65,209,255,0.08);
+  }
+
   .stash-create {
     display: grid;
     grid-template-columns: minmax(0, 1fr) auto auto;
@@ -1585,7 +1635,8 @@
   .branch-info strong { display: block; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; font-size: 13px; color: var(--color-ink); }
   .branch-info span { display: block; margin-top: 2px; color: var(--color-ink-dim); font-size: 11px; }
 
-  .branch-actions { display: flex; align-items: center; justify-content: flex-end; gap: 5px; }
+  .branch-actions { display: flex; align-items: center; justify-content: flex-end; flex-wrap: wrap; gap: 5px; }
+  .branch-actions .btn-sm { min-height: 24px; padding: 0 6px; font-size: 11px; }
 
   .branch-context-menu,
   .explorer-context-menu {
@@ -3687,6 +3738,7 @@
   .history-resize-handle { display: none; }
   .shell-body     { gap: 6px; }
   .left-sidebar   { gap: 6px; grid-template-rows: minmax(150px, 0.7fr) minmax(145px, 0.55fr) minmax(190px, 1fr); }
+  .left-sidebar:has(.stash-panel.collapsed) { grid-template-rows: minmax(150px, 0.8fr) auto minmax(190px, 1.1fr); }
   .section-head   { min-height: 40px; padding: 6px 10px; }
   .repo-summary   { height: 40px; padding: 0 10px; }
   .repo-branch    { max-width: 160px; }
@@ -3704,6 +3756,7 @@
   .workspace      { grid-template-columns: 1fr; gap: 6px; }
   .history-aside  { grid-template-columns: 1fr; grid-template-rows: minmax(200px, 1fr) minmax(150px, 0.5fr); min-height: 380px; }
   .left-sidebar   { grid-template-rows: minmax(180px, 0.9fr) minmax(150px, 0.55fr) minmax(220px, 1fr); min-height: 560px; }
+  .left-sidebar:has(.stash-panel.collapsed) { grid-template-rows: minmax(180px, 1fr) auto minmax(220px, 1.1fr); }
   .top-section    { grid-template-columns: minmax(0, 1fr); grid-template-rows: minmax(0, 1fr) 14px var(--commit-panel-height, 190px); }
   .repo-form      { grid-template-columns: 1fr; }
   .repo-tabbar    { grid-template-columns: minmax(0, 1fr) auto; }