feat: save short cut image to remote by ssh

- add settings for ssh config
- implement save remote function by ssh

internal/domain/config.go

@@ -1,8 +1,8 @@
 // Package domain — configuration types.
 //
-// S3Config is intentionally split into its own file so that future providers
-// can introduce their own configuration types side-by-side without polluting
-// the core domain types file.
+// 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.
 package domain
 
 // S3Config describes the connection parameters for any S3-compatible
@@ -27,10 +27,41 @@ type S3Config struct {
 	UsePathStyle    bool   `json:"usePathStyle"`
 }
 
+// SSHConfig describes the parameters required to upload a screenshot via
+// SSH/SCP to a remote host.
+//
+// Field design notes:
+//   - Host / Port form the destination endpoint. Port defaults to 22 when 0.
+//   - User is the SSH login name.
+//   - Password is optional; when empty the implementation falls back to the
+//     local SSH agent or ~/.ssh/id_* keys (i.e. the user is responsible for
+//     having password-less access already configured on this machine).
+//   - PathPrefix is interpreted *relative to the remote user's $HOME*. The
+//     UI presents it as "~/<PathPrefix>" so the user cannot escape the home
+//     directory by writing absolute paths. Leading "/" or "~" markers are
+//     stripped before the path is used.
+//   - StrictHostKey toggles host key verification. When false the client
+//     uses ssh.InsecureIgnoreHostKey() to mimic `scp -o StrictHostKeyChecking=no`,
+//     trading some security for first-launch usability on personal LANs.
+//   - KnownHostsPath defaults to ~/.ssh/known_hosts when empty and is only
+//     used while StrictHostKey is true.
+//   - ConnectTimeoutSecs caps the network handshake duration so a wrong
+//     endpoint does not hang the capture flow indefinitely.
+type SSHConfig struct {
+	Host               string `json:"host"`
+	Port               int    `json:"port"`
+	User               string `json:"user"`
+	Password           string `json:"password"`
+	PathPrefix         string `json:"pathPrefix"`
+	StrictHostKey      bool   `json:"strictHostKey"`
+	KnownHostsPath     string `json:"knownHostsPath"`
+	ConnectTimeoutSecs int    `json:"connectTimeoutSecs"`
+}
+
 // AppConfig is the top-level on-disk configuration document.
 //
-// We keep S3 nested so that adding more providers later (e.g. AliyunOSS, COS)
-// only requires a new sibling field rather than a schema rewrite.
+// 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.
 type AppConfig struct {
 	// Hotkey describes the global shortcut that triggers a capture.
 	// Stored as a human-readable string like "cmd+shift+a"; parsing happens
@@ -39,6 +70,10 @@ type AppConfig struct {
 
 	// S3 holds the active S3-compatible storage configuration.
 	S3 S3Config `json:"s3"`
+
+	// SSH holds the configuration for the optional "save to remote via scp"
+	// destination triggered by the save-remote toolbar button.
+	SSH SSHConfig `json:"ssh"`
 }
 
 // DefaultAppConfig returns sane zero-value defaults used on first launch.
@@ -49,6 +84,12 @@ func DefaultAppConfig() AppConfig {
 			PathPrefix:   "snapgo/",
 			UsePathStyle: true,
 		},
+		SSH: SSHConfig{
+			Port:               22,
+			PathPrefix:         "snapgo/",
+			ConnectTimeoutSecs: 10,
+			StrictHostKey:      false,
+		},
 	}
 }
 
@@ -59,3 +100,10 @@ func (c AppConfig) IsS3Configured() bool {
 		c.S3.AccessKeyID != "" &&
 		c.S3.SecretAccessKey != ""
 }
+
+// IsSSHConfigured reports whether the SSH destination has the minimum
+// fields required to attempt a connection. Password is intentionally NOT
+// checked because empty password means "use agent / key auth".
+func (c AppConfig) IsSSHConfigured() bool {
+	return c.SSH.Host != "" && c.SSH.User != ""
+}