feat: save short cut image to remote by ssh

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

internal/infrastructure/ssh/uploader.go

@@ -0,0 +1,59 @@
+// uploader.go — small adapter that satisfies application.SSHUploader by
+// dialing a one-shot connection per upload. This keeps the application
+// layer free of any direct dependency on golang.org/x/crypto/ssh while
+// still exposing a clean, unit-testable contract.
+package ssh
+
+import (
+	"context"
+	"os"
+	"time"
+
+	"github.com/mmmy/snapgo/internal/domain"
+)
+
+// Uploader is the production implementation of application.SSHUploader.
+//
+// We dial fresh per-upload because:
+//   - Captures happen sparsely (a few per minute at peak), so the cost of
+//     a TCP+SSH handshake is dwarfed by user think-time.
+//   - Holding a long-lived connection would force us to add keepalives,
+//     reconnection logic, and config-change invalidation — not worth it
+//     for the current usage profile.
+type Uploader struct {
+	cfg domain.SSHConfig
+}
+
+// NewUploader returns a ready-to-use uploader. The configuration is
+// captured by value so a simultaneous in-flight upload cannot be re-
+// targeted by a settings save.
+func NewUploader(cfg domain.SSHConfig) *Uploader {
+	return &Uploader{cfg: cfg}
+}
+
+// Upload satisfies application.SSHUploader. We log entry/exit at INFO so
+// the operator sees a single line per upload in the normal happy path,
+// and ERROR with elapsed time when something fails.
+func (u *Uploader) Upload(ctx context.Context, remoteRelPath string, data []byte, mode os.FileMode) error {
+	start := time.Now()
+	sshLog().Info("uploader.Upload start",
+		"host", u.cfg.Host, "user", u.cfg.User, "port", u.cfg.Port,
+		"remote_path", remoteRelPath, "size", len(data))
+
+	client, err := Dial(ctx, u.cfg)
+	if err != nil {
+		sshLog().Error("uploader.Upload dial failed",
+			"host", u.cfg.Host, "elapsed", time.Since(start), "err", err)
+		return err
+	}
+	defer client.Close()
+	if err := client.CopyFile(ctx, remoteRelPath, data, mode); err != nil {
+		sshLog().Error("uploader.Upload copy failed",
+			"remote_path", remoteRelPath, "elapsed", time.Since(start), "err", err)
+		return err
+	}
+	sshLog().Info("uploader.Upload done",
+		"remote_path", remoteRelPath, "size", len(data),
+		"total_elapsed", time.Since(start))
+	return nil
+}