Minor Updates — Requires OpenPV 5.40.7 or higher

This patch fixes the C# demo apps drawing no text on OpenPV 5.40.7 and later. The extension library itself is unchanged.

• Demo font — the Bluetooth Classic and BLE demo apps now ship Font.ttf at the app root, where OpenPV's drawing library loads it; the 5.17.1 demos kept it in Assets/, which OpenPV 5.40.7 and later no longer read, so every label and button drew blank.
• Volume-down button — the Bluetooth Classic demo app's phone and headset panels now label the volume-down button with an en dash; the minus sign used before has no glyph in the demo font and drew as a blank button.
• Message time — the Bluetooth Classic demo app's Message Access panel now replaces the narrow no-break space that .NET puts before AM/PM, which the demo font can't draw.

If you already created a project from a 5.17.1 demo, you can fix it in place: move Assets/Font.ttf to the project root, and in the .csproj change <None Update="Assets\Font.ttf"> to <None Update="Font.ttf">.