拆分服务器地址配置为独立字段，支持CDN优选IP故障切换，新增重置数据库按钮

- model: ServerURL → Protocol/Host/ServerIPs/Port/Path 五个字段
- db: 自动迁移旧 server_url 列到新表结构
- ui: 配置窗口改为横向分组布局，保存失败时不再关闭窗口
- transport: 支持 TLS SNI + Host 头覆盖以连接 CDN 边缘节点
- session: CDN IP 列表连接失败自动切换到下一个
- 新增重置数据库按钮，一键清空所有配置

internal/i18n/en.toml

@@ -34,7 +34,7 @@ DlgDeleteProfileTitle = "Delete Profile"
 DlgDeleteProfileMsg = 'Delete profile "{{.name}}" and its stored credentials?'
 DlgProfileTitle = "Profile"
 DlgValidationTitle = "Validation"
-DlgValidationMsg = "Name, Server URL, and Username are required."
+DlgValidationMsg = "Name, Host, and Username are required."
 DlgDaemonError = "Daemon Error"
 DlgCredentialError = "Credential Error"
 DlgCredentialErrorMsg = "No password stored for this profile. Edit the profile to set it."
@@ -44,6 +44,10 @@ DlgSaveError = "Save Error"
 DlgKeychainError = "Keychain Error"
 DlgError = "Error"
 
+BtnResetDB = "Reset Database"
+DlgResetDBTitle = "Reset Database"
+DlgResetDBMsg = "Delete all profiles and connection logs? This cannot be undone."
+
 TrayShowWindow = "Show Window"
 TrayConnect = "Connect"
 TrayDisconnect = "Disconnect"
@@ -52,7 +56,11 @@ TrayLanguageAuto = "Auto"
 TrayQuit = "Quit"
 
 FieldName = "Name"
-FieldServerURL = "Server URL"
+FieldProtocol = "Protocol"
+FieldHost = "Host"
+FieldServerIPs = "Server IPs (CDN)"
+FieldPort = "Port"
+FieldPath = "Path"
 FieldUsername = "Username"
 FieldPassword = "Password"
 FieldAuthMode = "Auth Mode"
@@ -63,6 +71,7 @@ FieldMTUOverride = "MTU Override"
 PlaceholderCIDRs = "10.0.0.0/8, 172.16.0.0/12"
 PlaceholderMTU = "0 = use server MTU"
 PlaceholderPasswordUnchanged = "(unchanged)"
+PlaceholderServerIPs = "e.g. 1.2.3.4, 5.6.7.8"
 
 AuthModeBoth = "Both (JWT + Password)"
 AuthModeJWT = "JWT"