feat: display ASCII banner on TUI startup

cmd/sidekick-tui/main.go

@@ -39,6 +39,12 @@ var (
   userStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("6")).Bold(true)
   agentStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("5")).Bold(true)
   sysStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("8")).Italic(true)
+
+  banner = `        _      __        __     _         __
+  ___  (_) ___/ / ___   / /__  (_) ____  / /__
+ (_-< / / / _  / / -_) /  '_/ / / / __/ /  '_/
+/___//_/  \_,_/  \__/ /_/\_\ /_/  \__/ /_/\_\
+----------------------------------------------`
 )
 
 type model struct {
@@ -106,7 +112,7 @@ func initialModel() model {
     textarea: ta,
     agent:    agent,
     pool:     pool,
-    history:  []sidekick.Message{{Role: sidekick.MessageRoleSystem, Content: "Sidekick initialized. Type a message below."}},
+    history:  []sidekick.Message{{Role: sidekick.MessageRoleSystem, Content: banner + "\n\nSidekick initialized. Type a message below."}},
   }
 }
 

cmd/sidekick-tui/tui_test.go

@@ -27,6 +27,9 @@ func TestInitialModel(t *testing.T) {
 	if len(m.history) != 1 {
 		t.Errorf("expected 1 initial message in history, got %d", len(m.history))
 	}
+	if !strings.Contains(m.history[0].Content, "Sidekick initialized") {
+		t.Error("expected initial message content to contain 'Sidekick initialized'")
+	}
 }
 
 func TestModelUpdate(t *testing.T) {