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>

ui/model.go

@@ -0,0 +1,48 @@
+package ui
+
+import (
+	tea "github.com/charmbracelet/bubbletea"
+)
+
+type screen int
+
+const (
+	screenTitle screen = iota
+)
+
+type Model struct {
+	width       int
+	height      int
+	fingerprint string
+	screen      screen
+}
+
+func NewModel(width, height int, fingerprint string) Model {
+	return Model{
+		width:       width,
+		height:      height,
+		fingerprint: fingerprint,
+		screen:      screenTitle,
+	}
+}
+
+func (m Model) Init() tea.Cmd {
+	return nil
+}
+
+func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
+	switch msg := msg.(type) {
+	case tea.KeyMsg:
+		if msg.String() == "q" || msg.String() == "ctrl+c" {
+			return m, tea.Quit
+		}
+	case tea.WindowSizeMsg:
+		m.width = msg.Width
+		m.height = msg.Height
+	}
+	return m, nil
+}
+
+func (m Model) View() string {
+	return "Welcome to Catacombs!\n\nPress q to quit."
+}