refactor: remove Favorites and Untagged from sidebar

- Remove Favorites NavItem, Star icon import, go-favorites command
- Remove Untagged NavItem, TagSimple icon import
- Remove favorites from SidebarFilter union type
- Update tests: Sidebar.test.tsx, useMenuEvents.test.ts, App.test.tsx
- Remove GO_FAVORITES constant and menu item from menu.rs

src/hooks/useMenuEvents.test.ts

@@ -226,12 +226,6 @@ describe('dispatchMenuEvent', () => {
     expect(h.onSelectFilter).toHaveBeenCalledWith('all')
   })
 
-  it('go-favorites selects favorites filter', () => {
-    const h = makeHandlers()
-    dispatchMenuEvent('go-favorites', h)
-    expect(h.onSelectFilter).toHaveBeenCalledWith('favorites')
-  })
-
   it('go-archived selects archived filter', () => {
     const h = makeHandlers()
     dispatchMenuEvent('go-archived', h)