Implement Cast Streaming mirroring, DLNA casting, daemon+GUI, and breadd integration

Builds out the full v1 scope: a vendored+patched openscreen subset for
low-latency Cast Streaming (Mirroring receiver 0F5096E8) alongside the
existing Cast V2/HLS and new DLNA/AVTransport casting paths, breadcastd's
Idle/Casting state machine with a private IPC socket, the breadcast GTK4
popup as a thin IPC client, and bread.cast.*/bread.command.cast.* breadd
integration (device discovery, start/stop, mirroring lifecycle events).
Also adds bakery/systemd/Forgejo CI packaging.

Validated end-to-end against a real Chromecast/Google TV: negotiated
Cast Streaming session, live pipeline playback, and daemon+GUI click-to-cast/
stop through the actual popup.

breadcast-caststream-sys/vendor/openscreen/platform/impl/socket_state.h

@@ -0,0 +1,37 @@
+// Copyright 2019 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef PLATFORM_IMPL_SOCKET_STATE_H_
+#define PLATFORM_IMPL_SOCKET_STATE_H_
+
+#include <cstdint>
+#include <memory>
+#include <string>
+
+namespace openscreen {
+
+// TcpSocketState should be used by TCP and TLS sockets for indicating
+// current state. NOTE: socket state transitions should only happen in
+// the listed order. New states should be added in appropriate order.
+enum class TcpSocketState {
+  // Socket is not connected.
+  kNotConnected = 0,
+
+  // Socket is actively listening for incoming connections.
+  kListening,
+
+  // Socket is currently being connected.
+  kConnecting,
+
+  // Socket is actively connected to a remote address.
+  kConnected,
+
+  // The socket connection has been terminated, either by Close() or
+  // by the remote side.
+  kClosed
+};
+
+}  // namespace openscreen
+
+#endif  // PLATFORM_IMPL_SOCKET_STATE_H_