implement basic tab navigation

bubbletea.go

@@ -34,6 +34,16 @@ func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
             if m.cursor < len(m.todos)-1 {
                 m.cursor++
             }
+		
+		case "left", "h":
+			if m.tab > 0 {
+				m.tab--
+			}
+
+		case "right", "l":
+			if m.tab < 4 {
+				m.tab++
+			}
 
         // The "enter" key and the spacebar (a literal space) toggle
         // the selected state for the item that the cursor is pointing at.

model.go

@@ -6,6 +6,7 @@ type todo struct {
 	deadline	int
 	startdate	int
 	priority	int  // 1-4, 1 being highest priority, 4 being no priority
+	isInbox		bool
 }
 
 type model struct {