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/scoped_pipe.h

@@ -0,0 +1,71 @@
+// Copyright 2018 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_SCOPED_PIPE_H_
+#define PLATFORM_IMPL_SCOPED_PIPE_H_
+
+#include <unistd.h>
+
+#include <utility>
+
+namespace openscreen {
+
+struct IntFdTraits {
+  using PipeType = int;
+  static constexpr int kInvalidValue = -1;
+
+  static void Close(PipeType pipe) { close(pipe); }
+};
+
+// This class wraps file descriptor and uses RAII to ensure it is closed
+// properly when control leaves its scope.  It is parameterized by a traits type
+// which defines the value type of the file descriptor, an invalid value, and a
+// closing function.
+//
+// This class is move-only as it represents ownership of the wrapped file
+// descriptor.  It is not thread-safe.
+template <typename Traits>
+class ScopedPipe {
+ public:
+  using PipeType = typename Traits::PipeType;
+
+  ScopedPipe() : pipe_(Traits::kInvalidValue) {}
+  explicit ScopedPipe(PipeType pipe) : pipe_(pipe) {}
+  ScopedPipe(const ScopedPipe&) = delete;
+  ScopedPipe(ScopedPipe&& other) : pipe_(other.release()) {}
+  ~ScopedPipe() {
+    if (pipe_ != Traits::kInvalidValue)
+      Traits::Close(release());
+  }
+
+  ScopedPipe& operator=(ScopedPipe&& other) {
+    if (pipe_ != Traits::kInvalidValue)
+      Traits::Close(release());
+    pipe_ = other.release();
+    return *this;
+  }
+
+  PipeType get() const { return pipe_; }
+  PipeType release() {
+    PipeType pipe = pipe_;
+    pipe_ = Traits::kInvalidValue;
+    return pipe;
+  }
+
+  bool operator==(const ScopedPipe& other) const {
+    return pipe_ == other.pipe_;
+  }
+  bool operator!=(const ScopedPipe& other) const { return !(*this == other); }
+
+  explicit operator bool() const { return pipe_ != Traits::kInvalidValue; }
+
+ private:
+  PipeType pipe_;
+};
+
+using ScopedFd = ScopedPipe<IntFdTraits>;
+
+}  // namespace openscreen
+
+#endif  // PLATFORM_IMPL_SCOPED_PIPE_H_