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

tests/test_waveform.py

@@ -122,5 +122,30 @@ def test_find_pauses_returns_list():
         # The first silence should start near 0 and end near 5
         assert pauses[0][0] < 1.0
         assert pauses[0][1] > 4.0
+    finally:
+        path.unlink(missing_ok=True)
+
+
+def test_render_multiband_smoke():
+    """render_multiband_waveform: 6-sec audio, 3 bands of 2 sec each → 3 rows."""
+    from sermon_clean.waveform import render_multiband_waveform
+    import tempfile, subprocess
+    with tempfile.NamedTemporaryFile(suffix=".wav", delete=False) as f:
+        path = Path(f.name)
+    try:
+        # 6-sec 440Hz tone
+        subprocess.run([
+            "ffmpeg", "-y", "-v", "error",
+            "-f", "lavfi", "-i", "sine=frequency=440:duration=6",
+            str(path),
+        ], check=True)
+        result = render_multiband_waveform(path, width=30, band_seconds=2.0)
+        band_lines = [line for line in result.splitlines() if "|" in line]
+        # 6-sec audio at 2-sec bands → 3 full bands + 1 partial = 4 rows
+        assert len(band_lines) in (3, 4), f"expected 3-4 bands, got {len(band_lines)}"
+        # First band should be labeled 0:00
+        assert band_lines[0].startswith("0:00")
+        # Second should be 0:02
+        assert band_lines[1].startswith("0:02")
     finally:
         path.unlink(missing_ok=True)