feat(git-status): group changed files under collapsible folders (setting, default on)

The Git window shows each group's files under their folders, collapsed until clicked, with single-child folder chains merged and open folders surviving the refresh. App Settings → Bottom bar → 'Git status: group files by folder' (per device) switches back to the flat list.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JrzFKEdBLwVfu6ev2ZscJS

src/web/public/index.html

@@ -1965,6 +1965,13 @@
                     </div>
                     <label class="switch switch-sm"><input type="checkbox" id="appSettingsShowGitStatus"><span class="slider"></span></label>
                   </div>
+                  <div class="set-row" data-search="git status folders tree flat list collapsed expand files">
+                    <div class="set-row-text">
+                      <span class="set-row-label">Git status: group files by folder <span class="set-scope">device</span></span>
+                      <span class="set-row-desc">In the Git window, show changed files under their folders, collapsed until you click a folder. Off lists every file by its full path. On by default.</span>
+                    </div>
+                    <label class="switch switch-sm"><input type="checkbox" id="appSettingsGitStatusTree" checked><span class="slider"></span></label>
+                  </div>
                 </div>
               </div>