Add scripttest-based integration tests (#59)

- Complete test coverage for all major bd commands:
  blocked, close, create, dep (add/remove/tree), export, help,
  import, init, list, quickstart, ready, show, stats, update, version
- Test data files validate command behavior and output
- Enables automated testing of full CLI workflows

cmd/bd/scripttest_test.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"context"
+	"os/exec"
+	"testing"
+	"time"
+
+	"rsc.io/script"
+	"rsc.io/script/scripttest"
+)
+
+func TestScripts(t *testing.T) {
+	// Build the bd binary
+	exe := t.TempDir() + "/bd"
+	if err := exec.Command("go", "build", "-o", exe, ".").Run(); err != nil {
+		t.Fatal(err)
+	}
+
+	// Create minimal engine with default commands plus bd
+	engine := script.NewEngine()
+	engine.Cmds["bd"] = script.Program(exe, nil, 100*time.Millisecond)
+
+	// Run all tests
+	scripttest.Test(t, context.Background(), engine, nil, "testdata/*.txt")
+}