fix: skip duration read for active recordings to prevent garbage values

WAV nframes and FLAC total_samples are both unfinalized while the
recorder has the file open, producing wildly wrong durations
(e.g. 53375995583:39:01). Return None (shown as —) instead.

web.py

@@ -224,8 +224,12 @@ def list_files(recordings_dir: str):
             continue
         stat     = path.stat()
         rel      = str(path.relative_to(base)).replace('\\', '/')
+        is_active = rel in active_files
 
-        duration = _get_audio_duration(path)
+        # Skip reading partial headers for in-progress files — the WAV nframes
+        # field and FLAC total_samples are both unfinalized while recording,
+        # producing wildly incorrect values (e.g. 53375995583:39:01).
+        duration = None if is_active else _get_audio_duration(path)
 
         files.append({
             'name':      rel,
@@ -234,7 +238,7 @@ def list_files(recordings_dir: str):
             'date':      datetime.fromtimestamp(stat.st_mtime).strftime('%Y-%m-%d %H:%M:%S'),
             'duration':  duration,
             'ext':       path.suffix.lower().lstrip('.'),
-            'recording': rel in active_files,
+            'recording': is_active,
         })
 
     files.sort(key=lambda f: f['mtime'], reverse=True)