fix: simplify RunRemote to not re-prefix source or dest

RunRemote was adding user@host: prefixes on top of the paths already
pre-prefixed by engine.go in the remote-to-remote branch, causing
"both remote" rsync errors. The source path was also incorrectly
prefixed with srcUserHost:, making rsync reject the command entirely.

The fix: buildArgs already orders args correctly for rsync (source
then dest), so just use args[-2] and args[-1] as-is without any
additional prefixing.

internal/syncengine/rsync_runner.go

@@ -96,39 +96,16 @@ func (r *RsyncRunner) RunRemote(ctx context.Context, pair *SyncPairConfig, src *
 		destKey = filepath.Join(r.sshDir, "id_ed25519")
 	}
 
-	srcUserHost := fmt.Sprintf("%s@%s", src.SSHUser, src.Host)
 	args := r.buildArgs(pair)
 
 	innerSSH := fmt.Sprintf("ssh -i %s -o StrictHostKeyChecking=accept-new -o UserKnownHostsFile=%s",
 		destKey, filepath.Join(r.sshDir, "known_hosts"))
 	rsyncFlags := strings.Join(args[:len(args)-2], " ")
-
-	var sourcePath, destPath string
-	if pair.Direction == "pull" {
-		sourcePath = args[len(args)-1]
-		destPath = args[len(args)-2]
-	} else {
-		sourcePath = args[len(args)-2]
-		destPath = args[len(args)-1]
-	}
-
-	var remoteSrc, remoteDst string
-	if pair.Direction == "pull" {
-		remoteSrc = sourcePath
-		remoteDst = destPath
-		if !strings.Contains(destPath, "@") {
-			remoteDst = fmt.Sprintf("%s@%s:%s", dst.SSHUser, dst.Host, destPath)
-		}
-	} else {
-		remoteDst = destPath
-		if !strings.Contains(destPath, "@") {
-			remoteDst = fmt.Sprintf("%s@%s:%s", dst.SSHUser, dst.Host, destPath)
-		}
-		remoteSrc = fmt.Sprintf("%s:%s", srcUserHost, sourcePath)
-	}
+	sourcePath := args[len(args)-2]
+	destPath := args[len(args)-1]
 
 	remoteCmd := fmt.Sprintf("rsync %s -e %q %s %s",
-		rsyncFlags, innerSSH, remoteSrc, remoteDst)
+		rsyncFlags, innerSSH, sourcePath, destPath)
 
 	sshArgs := []string{
 		"-i", src.PrivKey,