Add clap detection sensitivity settings (Tools menu)

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.

scripts/detect_claps.py

@@ -11,7 +11,7 @@ from datetime import timedelta
 from pathlib import Path
 
 sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
-from clap_detection import detect_claps, ClapDetectionUnavailable
+from clap_detection import detect_claps, ClapDetectionUnavailable, DEFAULT_THRESHOLD, DEFAULT_MIN_INTERVAL
 
 
 def format_timestamp(seconds):
@@ -43,10 +43,10 @@ Threshold guide:
     )
 
     parser.add_argument('input_file', help='Audio or video file')
-    parser.add_argument('-t', '--threshold', type=float, default=0.7,
-                        help='Detection threshold (0-1, default: 0.7, higher = less sensitive)')
-    parser.add_argument('-m', '--min-interval', type=float, default=0.3,
-                        help='Minimum seconds between detections (default: 0.3)')
+    parser.add_argument('-t', '--threshold', type=float, default=DEFAULT_THRESHOLD,
+                        help=f'Detection threshold (0-1, default: {DEFAULT_THRESHOLD}, higher = less sensitive)')
+    parser.add_argument('-m', '--min-interval', type=float, default=DEFAULT_MIN_INTERVAL,
+                        help=f'Minimum seconds between detections (default: {DEFAULT_MIN_INTERVAL})')
     parser.add_argument('-s', '--show-strength', action='store_true',
                         help='Show onset strength values')