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>

main.go

@@ -0,0 +1,13 @@
+package main
+
+import (
+	"log"
+
+	"github.com/tolelom/catacombs/server"
+)
+
+func main() {
+	if err := server.Start("0.0.0.0", 2222); err != nil {
+		log.Fatal(err)
+	}
+}