Disable editor network bootstrap in builds; tune scenes and paint HUD panel

NetworkBootstrap now destroys itself outside the editor. Camera FOV/background
tweaks in Main, lobby light intensity, and paint HUD panel font/color polish.

Assets/Scenes/Lobby.unity

@@ -1073,7 +1073,7 @@ Light:
   serializedVersion: 12
   m_Type: 1
   m_Color: {r: 1, g: 1, b: 1, a: 1}
-  m_Intensity: 3
+  m_Intensity: 2
   m_Range: 10
   m_SpotAngle: 30
   m_InnerSpotAngle: 21.80208