Threshold and min-interval (the librosa delta/wait knobs) were only
ever tunable via the CLI's -t/-m flags. Added a Clap Detection
Settings dialog (Tools menu) with both as spin boxes, an explicit
Reset to Defaults button, and Cancel that leaves MainWindow's current
settings untouched.
Exposed DEFAULT_THRESHOLD=0.7/DEFAULT_MIN_INTERVAL=0.3 as named
constants in clap_detection.py so the CLI script, DetectWorker's
defaults, and the dialog's reset button all reference the same source
of truth instead of three copies of the same magic numbers that could
drift apart.
