Improve logging: named logger, rotation, richer format, remove use_log guards

- Add setup_logging() returning a named 'qbit-maid' logger with
  RotatingFileHandler (configurable size/backups) and a console handler
- Add log_torrent() helper for structured torrent context
- Replace basicConfig-based tor_log() with setup_logging()
- Remove redundant 'if self.use_log:' guards across qbit-maid.py,
  qlist.py, qprocess.py, qlogging.py (level filtering handles it)
- Document new logging options in config.toml.example and README

config.toml.example

@@ -8,6 +8,9 @@ password = "pass"
 use_log = true
 log_level = "INFO"
 log_path = "./qc.log"
+# Optional: log rotation (defaults shown)
+log_max_bytes = 5000000
+log_backup_count = 3
 
 [app_tags]
 protected_tag = "ipt"