Remove empty terminal black areas

- Hide the terminal output viewport when there are no output lines on a newly loaded level.
- Reduce the minimum output history height so short output does not create a large empty black panel.
- Use the pane surface color for the app background so normal spacing between cards is not black.

app/src/main/java/solutions/tretter/githugandroid/GitHugTheme.kt

@@ -3,10 +3,10 @@ package solutions.tretter.githugandroid
 import androidx.compose.material3.darkColorScheme
 import androidx.compose.ui.graphics.Color
 
-val AppBackground = Color(0xFF000000)
 val PanelPrimary = Color(0xFF121212)
 val PanelSecondary = Color(0xFF1E1E1E)
 val PanelTertiary = Color(0xFF262626)
+val AppBackground = PanelSecondary
 val TerminalBackground = Color(0xFF050505)
 val TextPrimary = Color(0xFFFFFFFF)
 val TextSecondary = Color(0xFFE6E6E6)
@@ -26,4 +26,4 @@ val GitHugColorScheme = darkColorScheme(
     surfaceVariant = PanelSecondary,
     onSurfaceVariant = TextSecondary,
     outline = TextMuted,
-)
+)