SimpleCast 0.9.0 beta 21

Beta 21 improves window stability and corrects the bitrate information sent to
Icecast servers.

Safer Windows frame

Restored the standard Windows-owned title bar, movement, resizing, minimize,
maximize, and close behavior. SimpleCast no longer implements these fragile
operations itself.
Uses Windows DWM colors to blend the native title bar with the selected
SimpleCast skin while retaining standard Windows behavior.
Removes the custom drag and resize path that could cause visual artifacts or
terminate the application while the window was being moved.
Keeps mini mode accessible through a dedicated MINI button and preserves its
compact layout using the same native frame.

Added a dedicated Icecast source uploader instead of relying on FFmpeg's
limited Icecast header support.
Icecast now receives the selected bitrate, output sample rate, and channel
count through Ice-Bitrate, Ice-Samplerate, Ice-Channels, and
Ice-Audio-Info source headers.
The server should now report 128, 192, or 320 kbps in agreement with the
selected SimpleCast quality preset.
The new upload path supports normal and multistream broadcasts, TLS,
authentication, reconnecting, and existing station information.

All 127 automated tests pass.
The 15-second 48 kHz stereo encoder soak and decode check pass.
The packaged Windows application builds successfully.
A native-frame smoke test is included for checking packaged builds without
replacing Windows' own window-management behavior.

The Windows beta artifacts are intentionally unsigned, so Windows may show a
SmartScreen or Smart App Control warning.