feat: waveform view/selection state + band/handle painting

tests/test_ui_structure.py

@@ -398,6 +398,22 @@ def test_waveform_strip_present_and_safe(win):
     win._on_wave_refresh()
 
 
+def test_waveform_view_and_selection(win):
+    w = win._wave
+    w.set_view(10.0, 4.0)
+    w.set_selection(11.0, 12.5)
+    assert w._view_start == 10.0 and w._view_dur == 4.0
+    assert w.selection() == (11.0, 12.5)
+    # selection clamps into the view window and keeps start < end
+    w.set_selection(9.0, 20.0)
+    s, e = w.selection()
+    assert s >= 10.0 and e <= 14.0 and s < e
+    w.set_peaks([0.1, 0.9, 0.3])   # still paints without crashing
+    w.set_playhead(11.5)
+    w.clear()                       # resets display state
+    assert w.selection() is None
+
+
 def test_audition_button_present_and_safe(win):
     from PyQt6.QtWidgets import QPushButton
     assert isinstance(win._btn_audio_play, QPushButton)