feat(audio dock): the shell — 168px, auto-collapsing, replacing the empty bottom bar

Unit 4 of the sound-bar refactor. `Controls/AudioDock` takes the bottom row that held the empty
`BottomBar` spacer (deleted): four bay containers (MIC / GAME / TRAX / LIP-SYNC) above a 36px
master strip, all token-styled.

Height comes from `Models/AudioDockLayout`, not from a setting: 168px normally, 36px below a 900px
window height. At the 1366×768 minimum a full dock leaves ~398px for the preview, so the collapse
is mandatory, not cosmetic. The dock listens to its window's SizeChanged and re-applies.

Nothing here pretends to be a meter yet — the bays and the master readouts fill in over the next
units, each with its own test.

Guard: AudioDockLayoutTests pins both sides of the threshold (768 collapsed, 1040 expanded), the
boundary itself, and the two heights as the design's numbers.

ytLive.Tests/AudioDockLayoutTests.cs

@@ -0,0 +1,32 @@
+using Xunit;
+using ytLive.Models;
+
+namespace ytLive.Tests;
+
+/// <summary>The dock's height is the whole reason it is allowed to take 168px: on a short window it
+/// must get out of the way instead of squeezing the preview. The threshold is the creator's
+/// minimum (768) and default (1040) — both sides are pinned here so a future "tidy" cannot leave a
+/// 768px window with a full dock.
+/// </summary>
+public class AudioDockLayoutTests
+{
+    [Fact]
+    public void The_dock_collapses_on_short_windows_and_expands_on_normal_ones()
+    {
+        // Minimum window: collapsed, so the preview keeps its room.
+        Assert.True(AudioDockLayout.IsCollapsed(768));
+        Assert.Equal(AudioDockLayout.CollapsedHeight, AudioDockLayout.HeightFor(768));
+
+        // Default window: the full dock.
+        Assert.False(AudioDockLayout.IsCollapsed(1040));
+        Assert.Equal(AudioDockLayout.ExpandedHeight, AudioDockLayout.HeightFor(1040));
+
+        // The boundary itself belongs to the expanded side (>= is the friendlier read).
+        Assert.False(AudioDockLayout.IsCollapsed(AudioDockLayout.CollapseBelowHeight));
+        Assert.True(AudioDockLayout.IsCollapsed(AudioDockLayout.CollapseBelowHeight - 1));
+
+        // The two heights are the design's numbers, not whatever looked fine.
+        Assert.Equal(168, AudioDockLayout.ExpandedHeight);
+        Assert.Equal(36, AudioDockLayout.CollapsedHeight);
+    }
+}