feat: add FTP and SFTP upload support

internal/domain/config.go

@@ -1,8 +1,8 @@
 // Package domain — configuration types.
 //
-// S3Config and SSHConfig are intentionally split into their own structs so
-// that future providers can introduce their own configuration types side-
-// by-side without polluting the core domain types file.
+// S3Config, SSHConfig, and FTPConfig are intentionally split into their own
+// structs so future providers can introduce configuration types side-by-side
+// without polluting the core domain types file.
 package domain
 
 // S3Config describes the connection parameters for any S3-compatible
@@ -72,6 +72,32 @@ type SSHConfig struct {
 	ConnectTimeoutSecs int    `json:"connectTimeoutSecs"`
 }
 
+// FTPConfig describes a file-transfer destination reached through FTP or
+// SFTP. It is intentionally separate from SSHConfig: SFTP uses the SSH
+// transport, but it is a different file-transfer protocol from the existing
+// SCP action and has its own remote-root semantics.
+//
+// Field design notes:
+//   - Protocol is either "ftp" or "sftp". Their default ports are 21 and 22.
+//   - AuthMethod is used only by SFTP. "password" uses Password, while "key"
+//     reuses the local ssh-agent and ~/.ssh/id_* discovery used by SSH/SCP.
+//   - PathPrefix is relative to the account's login root. The application
+//     rejects absolute paths and traversal segments before uploading.
+//   - StrictHostKey and KnownHostsPath apply only to SFTP. Plain FTP has no
+//     host-key mechanism and sends credentials and data without encryption.
+type FTPConfig struct {
+	Protocol           string `json:"protocol"`
+	Host               string `json:"host"`
+	Port               int    `json:"port"`
+	User               string `json:"user"`
+	AuthMethod         string `json:"authMethod"`
+	Password           string `json:"password"`
+	PathPrefix         string `json:"pathPrefix"`
+	StrictHostKey      bool   `json:"strictHostKey"`
+	KnownHostsPath     string `json:"knownHostsPath"`
+	ConnectTimeoutSecs int    `json:"connectTimeoutSecs"`
+}
+
 // LLMProviderConfig stores one OpenAI-compatible multimodal chat endpoint.
 //
 // The three built-in providers (Qwen, Doubao/Ark, OpenAI-compatible) all use
@@ -145,6 +171,12 @@ const (
 	SSHAuthKerberos = "kerberos"
 )
 
+// File-transfer protocol identifiers stored in FTPConfig.Protocol.
+const (
+	FTPProtocolFTP  = "ftp"
+	FTPProtocolSFTP = "sftp"
+)
+
 // Built-in LLM provider identifiers.
 const (
 	LLMProviderQwen   = "qwen"
@@ -181,8 +213,8 @@ func (c SSHConfig) IsKerberos() bool {
 
 // AppConfig is the top-level on-disk configuration document.
 //
-// We keep S3 / SSH nested so that adding more providers later (e.g. AliyunOSS,
-// COS, FTP) only requires a new sibling field rather than a schema rewrite.
+// We keep S3 / SSH / FTP nested so adding another provider later only requires
+// a new sibling field rather than a schema rewrite.
 type AppConfig struct {
 	// Hotkey describes the global shortcut that triggers a capture.
 	// Stored as a human-readable string like "cmd+shift+a"; parsing happens
@@ -199,6 +231,9 @@ type AppConfig struct {
 	// destination triggered by the save-remote toolbar button.
 	SSH SSHConfig `json:"ssh"`
 
+	// FTP holds the destination used by the dedicated FTP/SFTP toolbar action.
+	FTP FTPConfig `json:"ftp"`
+
 	// LLM holds provider settings for the "copy summary" screenshot action.
 	LLM LLMConfig `json:"llm"`
 
@@ -221,6 +256,14 @@ func DefaultAppConfig() AppConfig {
 			ConnectTimeoutSecs: 10,
 			StrictHostKey:      false,
 		},
+		FTP: FTPConfig{
+			Protocol:           FTPProtocolFTP,
+			Port:               21,
+			AuthMethod:         SSHAuthPassword,
+			PathPrefix:         "snapgo/",
+			ConnectTimeoutSecs: 10,
+			StrictHostKey:      false,
+		},
 		LLM: DefaultLLMConfig(),
 		OCR: DefaultOCRConfig(),
 	}
@@ -315,6 +358,25 @@ func (c *AppConfig) Normalize() {
 	if c.SSH.ConnectTimeoutSecs == 0 {
 		c.SSH.ConnectTimeoutSecs = 10
 	}
+	if c.FTP.Protocol != FTPProtocolFTP && c.FTP.Protocol != FTPProtocolSFTP {
+		c.FTP.Protocol = FTPProtocolFTP
+	}
+	if c.FTP.Port == 0 {
+		if c.FTP.Protocol == FTPProtocolSFTP {
+			c.FTP.Port = 22
+		} else {
+			c.FTP.Port = 21
+		}
+	}
+	if c.FTP.AuthMethod != SSHAuthPassword && c.FTP.AuthMethod != SSHAuthKey {
+		c.FTP.AuthMethod = SSHAuthPassword
+	}
+	if c.FTP.PathPrefix == "" {
+		c.FTP.PathPrefix = "snapgo/"
+	}
+	if c.FTP.ConnectTimeoutSecs == 0 {
+		c.FTP.ConnectTimeoutSecs = 10
+	}
 
 	defaultLLM := DefaultLLMConfig()
 	if c.LLM.ActiveProvider == "" {
@@ -409,6 +471,14 @@ func (c AppConfig) IsSSHConfigured() bool {
 	return c.SSH.Host != "" && c.SSH.User != ""
 }
 
+// IsFTPConfigured reports whether the FTP/SFTP destination has the minimum
+// fields required to attempt a connection. Password is not required because
+// SFTP key authentication and password-less FTP accounts are both valid.
+func (c AppConfig) IsFTPConfigured() bool {
+	return (c.FTP.Protocol == FTPProtocolFTP || c.FTP.Protocol == FTPProtocolSFTP) &&
+		c.FTP.Host != "" && c.FTP.User != ""
+}
+
 // ActiveLLMProvider returns the selected provider config plus a boolean
 // indicating whether the selection exists.
 func (c AppConfig) ActiveLLMProvider() (string, LLMProviderConfig, bool) {