feat: Task 15 — TUI Tab Framework + Orange Theme

- pkg/tui/styles.go — orange theme palette and component styles
- pkg/tui/tabs.go — Tab interface + TabManager with add/close/next/prev
- pkg/tui/host_list_tab.go — HostListTab implementing Tab interface
- pkg/tui/tui.go — refactored to use TabManager (backward compatible)
- pkg/tui/host_list.go — removed (logic moved to host_list_tab.go)
- pkg/tui/tui_test.go — adapted + added TabManager tests

pkg/tui/tui_test.go

@@ -10,13 +10,23 @@ func TestTUIInitialization(t *testing.T) {
 		t.Fatal("Failed to initialize TUI")
 	}
 
-	if ui.CurrentScreen != ScreenHostList {
-		t.Errorf("expected CurrentScreen ScreenHostList, got %d", ui.CurrentScreen)
+	if ui.tabs == nil {
+		t.Fatal("expected tabs manager to be initialized")
+	}
+
+	if ui.tabs.Len() != 1 {
+		t.Errorf("expected 1 tab, got %d", ui.tabs.Len())
 	}
 
 	if ui.Quit {
 		t.Error("expected Quit to be false")
 	}
+
+	// Should have a HostListTab by default
+	ht := FindHostListTab(ui.tabs.tabs)
+	if ht == nil {
+		t.Error("expected HostListTab to be the initial tab")
+	}
 }
 
 func TestTUILoadHosts(t *testing.T) {
@@ -29,4 +39,81 @@ func TestTUILoadHosts(t *testing.T) {
 	if ui.Hosts != nil {
 		t.Error("expected Hosts to be nil")
 	}
+
+	// Should still have a valid tab manager
+	if ui.tabs == nil {
+		t.Fatal("expected tabs manager to be valid")
+	}
+}
+
+func TestTabManagerBasic(t *testing.T) {
+	tm := NewTabManager(NewHostListTab())
+	if tm.Len() != 1 {
+		t.Errorf("expected 1 tab, got %d", tm.Len())
+	}
+
+	if tm.Active() == nil {
+		t.Fatal("expected active tab")
+	}
+
+	if tm.Active().Name() != "Hosts" {
+		t.Errorf("expected 'Hosts', got '%s'", tm.Active().Name())
+	}
+}
+
+func TestTabManagerNavigation(t *testing.T) {
+	tm := NewTabManager(NewHostListTab())
+
+	// Add a second tab
+	second := NewHostListTab()
+	tm.Add(second)
+	if tm.Len() != 2 {
+		t.Errorf("expected 2 tabs, got %d", tm.Len())
+	}
+
+	// Active should now be the last added tab
+	if tm.active != 1 {
+		t.Errorf("expected active index 1, got %d", tm.active)
+	}
+
+	// Previous
+	tm.Prev()
+	if tm.active != 0 {
+		t.Errorf("expected active index 0 after Prev, got %d", tm.active)
+	}
+
+	// Next
+	tm.Next()
+	if tm.active != 1 {
+		t.Errorf("expected active index 1 after Next, got %d", tm.active)
+	}
+}
+
+func TestTabManagerClose(t *testing.T) {
+	tm := NewTabManager(NewHostListTab())
+	second := NewHostListTab()
+	tm.Add(second)
+	tm.Add(NewHostListTab())
+
+	// Close active (last tab)
+	closed := tm.CloseActive()
+	if closed == nil {
+		t.Error("expected closed tab to be returned")
+	}
+
+	if tm.Len() != 2 {
+		t.Errorf("expected 2 tabs after close, got %d", tm.Len())
+	}
+
+	// Close all tabs except last
+	tm.Close(0)
+	if tm.Len() != 1 {
+		t.Errorf("expected 1 tab after close, got %d", tm.Len())
+	}
+
+	// Should not close the last tab via CloseActive (returns nil)
+	result := tm.CloseActive()
+	if result != nil {
+		t.Error("expected nil when trying to close the last tab")
+	}
 }