feat: implement basic TUI framework with host list

- Add Bubble Tea TUI model with Init/Update/View
- Implement host list screen with keyboard navigation (up/down/enter/q)
- Add styled rendering for hosts, selection, tags
- Create hostkeeper tui CLI command
- Add tests for TUI initialization and host loading
- Update project state documentation

pkg/tui/tui_test.go

@@ -0,0 +1,32 @@
+package tui
+
+import (
+	"testing"
+)
+
+func TestTUIInitialization(t *testing.T) {
+	ui := New()
+	if ui == nil {
+		t.Fatal("Failed to initialize TUI")
+	}
+
+	if ui.CurrentScreen != ScreenHostList {
+		t.Errorf("expected CurrentScreen ScreenHostList, got %d", ui.CurrentScreen)
+	}
+
+	if ui.Quit {
+		t.Error("expected Quit to be false")
+	}
+}
+
+func TestTUILoadHosts(t *testing.T) {
+	ui := New()
+	if ui == nil {
+		t.Fatal("Failed to initialize TUI")
+	}
+
+	ui.LoadHosts(nil)
+	if ui.Hosts != nil {
+		t.Error("expected Hosts to be nil")
+	}
+}