feat: project scaffold with SSH server and placeholder TUI

Sets up Go module, Wish/BubbleTea SSH server on port 2222, placeholder
TUI model showing "Welcome to Catacombs!", Dockerfile, and docker-compose.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/ssh.go

@@ -0,0 +1,40 @@
+package server
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/charmbracelet/ssh"
+	"github.com/charmbracelet/wish"
+	"github.com/charmbracelet/wish/bubbletea"
+	tea "github.com/charmbracelet/bubbletea"
+	gossh "golang.org/x/crypto/ssh"
+	"github.com/tolelom/catacombs/ui"
+)
+
+func Start(host string, port int) error {
+	s, err := wish.NewServer(
+		wish.WithAddress(fmt.Sprintf("%s:%d", host, port)),
+		wish.WithHostKeyPath(".ssh/catacombs_host_key"),
+		wish.WithPublicKeyAuth(func(_ ssh.Context, _ ssh.PublicKey) bool {
+			return true // accept all keys
+		}),
+		wish.WithMiddleware(
+			bubbletea.Middleware(func(s ssh.Session) (tea.Model, []tea.ProgramOption) {
+				pty, _, _ := s.Pty()
+				fingerprint := ""
+				if s.PublicKey() != nil {
+					fingerprint = gossh.FingerprintSHA256(s.PublicKey())
+				}
+				m := ui.NewModel(pty.Window.Width, pty.Window.Height, fingerprint)
+				return m, []tea.ProgramOption{tea.WithAltScreen()}
+			}),
+		),
+	)
+	if err != nil {
+		return fmt.Errorf("could not create server: %w", err)
+	}
+
+	log.Printf("Starting SSH server on %s:%d", host, port)
+	return s.ListenAndServe()
+}