feat(branches): add bulk delete for branch folders

Add a context-menu action to delete all branches in a folder at once.
Top-level remote folders are protected and the currently checked-out branch
is preserved. The BranchPanel API now includes folder depth to prevent
accidental bulk-deletes and summarizes individual failures after processing.
UI polish and localization were applied, and the package/version metadata,
changelog, and help overlay were updated for the 2026.8.4 release.

- Bulk delete with top-level remote protection and failure summaries.
- BranchPanel now tracks folder depth and disables unsafe context menus.
- Version bump, changelog/help overlay updates, and UI/localization tweaks.

src/app.css

@@ -1116,14 +1116,15 @@
     display: grid;
     place-items: center;
     align-self: center;
-    min-width: 24px;
-    width: 24px;
-    min-height: 24px;
-    height: 24px;
-    flex: 0 0 24px;
-    aspect-ratio: 1;
+    min-width: 26px;
+    width: 26px;
+    max-width: 26px;
+    min-height: 26px;
+    height: 26px;
+    max-height: 26px;
+    flex: 0 0 26px;
     margin-right: 6px;
-    border-radius: 50%;
+    border-radius: 5px;
     opacity: 0.58;
     transition: opacity 120ms ease, color 120ms ease, background 120ms ease;
   }