chore: 初始提交 Fonu 1.0.2

- 公网反代：Nginx 状态卡片（版本 / 运行状态 / 配置校验 / 端口监听）
- 部署设置第一、二梯队（HTTPS 开关、安全头、限流、连接数、仅中国大陆 IP）
- 隧道检测兼容 frps v0.68 / v0.71（V2 与旧版端点）
- 恢复被清空的 internal/frp/store.go、internal/api/ddns_handler.go、web/src/views/DdnsView.vue

internal/secret/secret.go

@@ -0,0 +1,84 @@
+package secret
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+)
+
+var ErrEmpty = errors.New("secret is empty")
+
+type Box struct {
+	gcm cipher.AEAD
+}
+
+func NewBox(keyMaterial string) (*Box, error) {
+	if keyMaterial == "" {
+		return nil, fmt.Errorf("encryption key material is required")
+	}
+	sum := sha256.Sum256([]byte(keyMaterial))
+	block, err := aes.NewCipher(sum[:])
+	if err != nil {
+		return nil, err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+	return &Box{gcm: gcm}, nil
+}
+
+func (b *Box) Encrypt(plain string) (string, error) {
+	if plain == "" {
+		return "", ErrEmpty
+	}
+	nonce := make([]byte, b.gcm.NonceSize())
+	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
+		return "", err
+	}
+	ciphertext := b.gcm.Seal(nonce, nonce, []byte(plain), nil)
+	return base64.StdEncoding.EncodeToString(ciphertext), nil
+}
+
+func (b *Box) Decrypt(encoded string) (string, error) {
+	if encoded == "" {
+		return "", ErrEmpty
+	}
+	raw, err := base64.StdEncoding.DecodeString(encoded)
+	if err != nil {
+		return "", err
+	}
+	nonceSize := b.gcm.NonceSize()
+	if len(raw) < nonceSize {
+		return "", fmt.Errorf("invalid ciphertext")
+	}
+	nonce, ciphertext := raw[:nonceSize], raw[nonceSize:]
+	plain, err := b.gcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return "", err
+	}
+	return string(plain), nil
+}
+
+func IsDecryptFailure(err error) bool {
+	if err == nil {
+		return false
+	}
+	return strings.Contains(err.Error(), "message authentication failed")
+}
+
+func DecryptHint(err error) error {
+	if err == nil {
+		return nil
+	}
+	if IsDecryptFailure(err) {
+		return fmt.Errorf("DNS API 凭据无法解密，请在 DDNS 页面重新保存 API Token（服务加密密钥可能已变更）")
+	}
+	return err
+}