Add multiband waveform view

- waveform.py: render_multiband_waveform() — N rows of ASCII bars, each row
  labeled with its band-start time. Makes it easy to find timestamps in
  long audio by counting row + column.
- cli.py: new 'multiband' / 'mb' subcommand
- Fixed: multiband band alignment was drifting (off-by-one in samples)
- tests: 1 new multiband smoke test; 62 total all passing

sermon_clean/cli.py

@@ -164,6 +164,21 @@ def cmd_paste(args: argparse.Namespace) -> int:
     return 0
 
 
+def cmd_multiband(args: argparse.Namespace) -> int:
+    """Print a multi-band ASCII waveform. Each row is N seconds labeled."""
+    from .waveform import render_multiband_waveform
+    audio = Path(args.audio)
+    if not audio.exists():
+        print(f"error: {audio} not found", file=sys.stderr)
+        return 1
+    print(render_multiband_waveform(
+        audio,
+        width=args.width,
+        band_seconds=args.band_seconds,
+    ))
+    return 0
+
+
 def cmd_slices(args: argparse.Namespace) -> int:
     """Extract overlapping audio slices for manual review.
 
@@ -324,6 +339,13 @@ def main(argv: list[str] | None = None) -> int:
     p_paste.add_argument("--replacements", nargs="+", help="glob(s) for replacement MP3s in order")
     p_paste.set_defaults(func=cmd_paste)
 
+    # multiband (multi-row ASCII waveform with band labels)
+    p_mb = sub.add_parser("multiband", aliases=["mb"], help="Multi-band ASCII waveform with band-start labels")
+    p_mb.add_argument("audio")
+    p_mb.add_argument("--width", type=int, default=60, help="waveform width in columns per band")
+    p_mb.add_argument("--band-seconds", type=float, default=60.0, help="seconds of audio per band (one row)")
+    p_mb.set_defaults(func=cmd_multiband)
+
     # slices (extract overlapping audio chunks for manual review)
     p_slices = sub.add_parser("slices", help="Extract overlapping audio slices for manual review")
     p_slices.add_argument("audio")