feat: Stage 1 scaffold — config, API client, placeholder TUI

Sets up the full project structure following the hactl/gokapi-tui
architecture: strict Elm-pattern Bubbletea TUI, YAML config at
~/.config/terdut-tui/config.yaml, REST API client with Bearer auth,
self-update via GitHub Releases, and a three-section tab placeholder
(Alerts / Schedule / Users) that verifies server connectivity on startup.

main.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	tea "github.com/charmbracelet/bubbletea"
+	"github.com/yeniklas/terdut-tui/internal/api"
+	"github.com/yeniklas/terdut-tui/internal/config"
+	"github.com/yeniklas/terdut-tui/internal/tui"
+	"github.com/yeniklas/terdut-tui/internal/updater"
+)
+
+var version = "dev"
+
+func main() {
+	versionFlag := flag.Bool("version", false, "print version and exit")
+	updateFlag := flag.Bool("self-update", false, "update terdut-tui to the latest release")
+	flag.Parse()
+
+	if *versionFlag {
+		fmt.Println(version)
+		os.Exit(0)
+	}
+
+	if *updateFlag {
+		if err := updater.Run(version); err != nil {
+			fmt.Fprintln(os.Stderr, "update:", err)
+			os.Exit(1)
+		}
+		os.Exit(0)
+	}
+
+	cfg, err := config.Load()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
+	client := api.NewClient(cfg.ServerURL, cfg.APIKey)
+	model := tui.NewModel(client, cfg.ServerURL, cfg.RefreshInterval)
+
+	p := tea.NewProgram(model, tea.WithAltScreen())
+	if _, err := p.Run(); err != nil {
+		fmt.Fprintln(os.Stderr, "error:", err)
+		os.Exit(1)
+	}
+}