feat(protbot): add headless MHF protocol bot as cmd/protbot

Copy MHBridge into the Erupe module as cmd/protbot/ so it can be
built, tested, and maintained alongside the server. The bot
implements the full sign → entrance → channel login flow and
supports lobby entry, chat, session setup, and quest enumeration.

The conn/ package keeps its own Blowfish crypto primitives to avoid
importing erupe-ce/config (which requires a config file at init).

cmd/protbot/conn/bin8_test.go

@@ -0,0 +1,52 @@
+package conn
+
+import (
+	"testing"
+)
+
+// TestCalcSum32 verifies the checksum against a known input.
+func TestCalcSum32(t *testing.T) {
+	// Verify determinism: same input gives same output.
+	data := []byte("Hello, MHF!")
+	sum1 := CalcSum32(data)
+	sum2 := CalcSum32(data)
+	if sum1 != sum2 {
+		t.Fatalf("CalcSum32 not deterministic: %08X != %08X", sum1, sum2)
+	}
+
+	// Different inputs produce different outputs (basic sanity).
+	data2 := []byte("Hello, MHF?")
+	sum3 := CalcSum32(data2)
+	if sum1 == sum3 {
+		t.Fatalf("CalcSum32 collision on different inputs: both %08X", sum1)
+	}
+}
+
+// TestDecryptBin8RoundTrip verifies that encrypting and decrypting with Bin8
+// produces the original data. We only have DecryptBin8, but we can verify
+// the encrypt→decrypt path by implementing encrypt inline here.
+func TestDecryptBin8RoundTrip(t *testing.T) {
+	original := []byte("Test data for Bin8 encryption round-trip")
+	key := byte(0x42)
+
+	// Encrypt (inline copy of Erupe's EncryptBin8)
+	k := uint32(key)
+	encrypted := make([]byte, len(original))
+	for i := 0; i < len(original); i++ {
+		rotate(&k)
+		tmp := bin8Key[i&7] ^ byte((k>>13)&0xFF)
+		encrypted[i] = original[i] ^ tmp
+	}
+
+	// Decrypt
+	decrypted := DecryptBin8(encrypted, key)
+
+	if len(decrypted) != len(original) {
+		t.Fatalf("length mismatch: got %d, want %d", len(decrypted), len(original))
+	}
+	for i := range original {
+		if decrypted[i] != original[i] {
+			t.Fatalf("byte %d: got 0x%02X, want 0x%02X", i, decrypted[i], original[i])
+		}
+	}
+}