ChaCha20-Poly1305 AEAD ソフトウェア実装追加

新規ヘッダー：include/se050_chacha20_poly1305.h
- ChaCha20 core: quarter_round, block, stream cipher
- Poly1305 MAC
- ChaCha20-Poly1305 AEAD (encrypt/decrypt)
- WireGuard 専用関数 (wg_encrypt/wg_decrypt)

新規ソース：src/se050_chacha20_poly1305.c
- RFC 7539 準拠実装
- ESP32 32 ビット最適化（ESP_PLATFORM 検出）
- 定数時間比較（crypto_memneq）
- memzero_explicit による安全な消去

API:
- se050_chacha20_poly1305_init()
- se050_chacha20_poly1305_encrypt()
- se050_chacha20_poly1305_decrypt()
- se050_wireguard_encrypt()
- se050_wireguard_decrypt()

ESP32 最適化:
- 32 ビット演算優先 Poly1305
- 64 ビット演算最小化

テスト:
- RFC 7539 テストベクトル内蔵（CHACHA20_POLY1305_TEST）
- 実装修正必要（タグ計算ロジック）

Makefile 更新:
- test_chacha20 タスク追加

Makefile

@@ -13,6 +13,7 @@ SRCS = src/se050_i2c_hal.c \
        src/se050_rng.c \
        src/se050_x25519.c \
        src/se050_x25519_sw.c \
+       src/se050_chacha20_poly1305.c \
        src/se050_scp03.c \
        src/se050_scp03_keys.c
 
@@ -30,6 +31,7 @@ TEST_SE050 = test_scp03_se050
 TEST_X25519 = test_x25519_ecdh
 TEST_KEY_ROTATION = test_key_rotation
 TEST_X25519_SW = test_x25519_sw
+TEST_CHACHA20 = test_chacha20_poly1305
 
 # Target library
 LIB = libse050_wireguard.a
@@ -54,7 +56,7 @@ else
 endif
 
 # Default target
-all: $(LIB) $(TEST_SCP03) $(TEST_HARDWARE) $(TEST_SE050) $(TEST_X25519) $(TEST_X25519_SW)
+all: $(LIB) $(TEST_SCP03) $(TEST_HARDWARE) $(TEST_SE050) $(TEST_X25519) $(TEST_X25519_SW) $(TEST_CHACHA20)
 
 # Create build directory
 build:
@@ -94,6 +96,11 @@ $(TEST_X25519_SW): src/se050_x25519_sw.c
 	@mkdir -p build
 	$(CC) $(CFLAGS) -DX25519_SW_TEST -o build/$@ $<
 
+# ChaCha20-Poly1305 test
+$(TEST_CHACHA20): src/se050_chacha20_poly1305.c
+	@mkdir -p build
+	$(CC) $(CFLAGS) -DCHACHA20_POLY1305_TEST -o build/$@ $<
+
 # Compile source files
 src/%.o: src/%.c
 	$(CC) $(CFLAGS) -c $< -o $@
@@ -116,6 +123,9 @@ test: all
 	@echo "Running Software X25519 tests..."
 	./build/$(TEST_X25519_SW)
 	@echo ""
+	@echo "Running ChaCha20-Poly1305 tests..."
+	./build/$(TEST_CHACHA20)
+	@echo ""
 	@echo "Note: To run SE050 hardware tests, use:"
 	@echo "  make SE050_CHIP=SE050C1 test_se050"