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/cast/streaming/resolution.h

@@ -0,0 +1,67 @@
+// Copyright 2021 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// Resolutions and dimensions (resolutions with a frame rate) are used
+// extensively throughout cast streaming. Since their serialization to and
+// from JSON is stable and standard, we have a single place definition for
+// these for use both in our public APIs and private messages.
+
+#ifndef CAST_STREAMING_RESOLUTION_H_
+#define CAST_STREAMING_RESOLUTION_H_
+
+#include "json/value.h"
+#include "util/simple_fraction.h"
+
+namespace openscreen::cast {
+
+// A resolution in pixels.
+struct Resolution {
+  static ErrorOr<Resolution> TryParse(const Json::Value& value);
+  bool IsValid() const;
+  Json::Value ToJson() const;
+
+  // Returns true if both `width` and `height` of this instance are greater than
+  // or equal to that of `other`.
+  bool IsSupersetOf(const Resolution& other) const;
+
+  bool operator==(const Resolution& other) const;
+  bool operator!=(const Resolution& other) const;
+
+  // Width and height in pixels.
+  int width = 0;
+  int height = 0;
+};
+
+// A resolution in pixels and a frame rate.
+struct Dimensions {
+  static ErrorOr<Dimensions> TryParse(const Json::Value& value);
+  bool IsValid() const;
+  Json::Value ToJson() const;
+
+  // Returns true if all properties of this instance are greater than or equal
+  // to those of `other`.
+  bool IsSupersetOf(const Dimensions& other) const;
+
+  bool operator==(const Dimensions& other) const;
+  bool operator!=(const Dimensions& other) const;
+
+  // Get just the width and height fields (for comparisons).
+  constexpr Resolution ToResolution() const { return {width, height}; }
+
+  // The effective bit rate is the width * height * frame rate.
+  constexpr int effective_bit_rate() const {
+    return width * height * static_cast<double>(frame_rate);
+  }
+
+  // Width and height in pixels.
+  int width = 0;
+  int height = 0;
+
+  // `frame_rate` is the maximum maintainable frame rate.
+  SimpleFraction frame_rate{0, 1};
+};
+
+}  // namespace openscreen::cast
+
+#endif  // CAST_STREAMING_RESOLUTION_H_