Replace split/unified and context controls with icon toggles, add a word-wrap toggle (default on), and move the toolbar into the tab header to free vertical space.
Render SplitFilePanel consistently and move empty/loading messages into the viewer area so the right drawer keeps its standard layout even when there are no session diffs, no git changes, or files are still loading.
Split InstanceShell2 into focused shell modules (drawer chrome/resize, session context/cache, sidebar, right panel tabs/components) to improve maintainability while preserving behavior.
