feat(05-02): add LEGAL.md, embed it, and wire keyhunter legal command

- Add LEGAL.md at repo root (109 lines) covering CFAA, Computer Misuse Act,
  EU Directive 2013/40/EU, responsible use, disclosure, and disclaimer.
- Mirror to pkg/legal/LEGAL.md for go:embed (Go cannot traverse parents).
- Add pkg/legal package exposing Text() for the embedded markdown.
- Add cmd/legal.go registering keyhunter legal subcommand to print it.

pkg/legal/legal_test.go

@@ -0,0 +1,22 @@
+package legal
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestText_NonEmpty(t *testing.T) {
+	got := Text()
+	if len(got) < 500 {
+		t.Fatalf("Text() too short: got %d bytes, want > 500", len(got))
+	}
+}
+
+func TestText_ContainsKeyPhrases(t *testing.T) {
+	got := Text()
+	for _, phrase := range []string{"CFAA", "Responsible Use", "Disclaimer"} {
+		if !strings.Contains(got, phrase) {
+			t.Errorf("Text() missing required phrase %q", phrase)
+		}
+	}
+}