Improve startup logging and logging consistency

Startup log:
- Add interface, port, and fileTransferPort fields to the "Hotline
  server started" line so operators can see what the server bound to.
- Resolve an empty -interface flag to 0.0.0.0 for display.

Levels:
- Demote the two Redis startup messages (ban management, cleared online
  users) from Info to Debug.

Consistency:
- Standardize the error field key to "err" (was "Err" in a few account
  handlers) and lowercase "Account" -> "account".
- Standardize the remote-address key to "remoteAddr" (was "RemoteAddr").
- Replace fmt.Sprintf in the tracker-registration message and string
  concatenation in the config-dir-init and ban-disconnect messages with
  structured fields; use the standard "err" key.
- Give the two bare rLogger.Error(err.Error()) file-transfer calls a
  descriptive message and an "err" field.

logger.go:
- Only attach the rotating lumberjack file writer when --log-file is set.
  An empty Filename made lumberjack write to a temp file by default.

1 files changed, 2 insertions, 2 deletions

diff --git a/hotline/file_transfer.go b/hotline/file_transfer.go
index 98999f1..86e10eb 100644
--- a/hotline/file_transfer.go
+++ b/hotline/file_transfer.go
@@ -477,7 +477,7 @@ func DownloadFolderHandler(rwc io.ReadWriter, fullPath string, fileTransfer *Fil
 
 		// Send file size to client
 		if _, err := rwc.Write(hlFile.Ffo.TransferSize(dataOffset)); err != nil {
-			rLogger.Error(err.Error())
+			rLogger.Error("Error sending file size", "err", err)
 			return fmt.Errorf("error sending file size: %w", err)
 		}
 
@@ -625,7 +625,7 @@ func UploadFolderHandler(rwc io.ReadWriter, fullPath string, fileTransfer *FileT
 				}
 
 				if err := receiveFile(rwc, file, io.Discard, io.Discard, fileTransfer.bytesSentCounter); err != nil {
-					rLogger.Error(err.Error())
+					rLogger.Error("Error receiving file", "err", err)
 				}
 
 				err = os.Rename(fullPath+"/"+fu.FormattedPath()+".incomplete", fullPath+"/"+fu.FormattedPath())