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/public/encoded_frame.h

@@ -0,0 +1,119 @@
+// Copyright 2014 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CAST_STREAMING_PUBLIC_ENCODED_FRAME_H_
+#define CAST_STREAMING_PUBLIC_ENCODED_FRAME_H_
+
+#include <stdint.h>
+
+#include <chrono>
+#include <vector>
+
+#include "cast/streaming/public/frame_id.h"
+#include "cast/streaming/rtp_time.h"
+#include "platform/api/time.h"
+#include "platform/base/span.h"
+
+namespace openscreen::cast {
+
+// A combination of metadata and data for one encoded frame.  This can contain
+// audio data or video data or other.
+struct EncodedFrame {
+  enum class Dependency : int8_t {
+    // "null" value, used to indicate whether `dependency` has been set.
+    kUnknown,
+
+    // Not decodable without the reference frame indicated by
+    // `referenced_frame_id`.
+    kDependent,
+
+    // Independently decodable.
+    kIndependent,
+
+    // Independently decodable, and no future frames will depend on any frames
+    // before this one.
+    kKeyFrame,
+  };
+
+  EncodedFrame(Dependency dependency,
+               FrameId frame_id,
+               FrameId referenced_frame_id,
+               RtpTimeTicks rtp_timestamp,
+               Clock::time_point reference_time,
+               std::chrono::milliseconds new_playout_delay,
+               Clock::time_point capture_begin_time,
+               Clock::time_point capture_end_time,
+               ByteView data);
+
+  // TODO(issuetracker.google.com/285905175): remove remaining optional fields
+  // (new_playout_delay) once Chrome provides the capture begin and end
+  // timestamps, so this constructor only provides the required fields.
+  EncodedFrame(Dependency dependency,
+               FrameId frame_id,
+               FrameId referenced_frame_id,
+               RtpTimeTicks rtp_timestamp,
+               Clock::time_point reference_time,
+               std::chrono::milliseconds new_playout_delay,
+               ByteView data);
+  EncodedFrame();
+  EncodedFrame(const EncodedFrame&) = delete;
+  EncodedFrame& operator=(const EncodedFrame&) = delete;
+  EncodedFrame(EncodedFrame&&) noexcept;
+  EncodedFrame& operator=(EncodedFrame&&);
+  ~EncodedFrame();
+
+  // Copies all members except `data` to `dest`. Does not modify |dest->data|.
+  void CopyMetadataTo(EncodedFrame* dest) const;
+
+  // This frame's dependency relationship with respect to other frames.
+  Dependency dependency = Dependency::kUnknown;
+
+  // The label associated with this frame.  Implies an ordering relative to
+  // other frames in the same stream.
+  FrameId frame_id;
+
+  // The label associated with the frame upon which this frame depends.  If
+  // this frame does not require any other frame in order to become decodable
+  // (e.g., key frames), `referenced_frame_id` must equal `frame_id`.
+  FrameId referenced_frame_id;
+
+  // The stream timestamp, on the timeline of the signal data. For example, RTP
+  // timestamps for audio are usually defined as the total number of audio
+  // samples encoded in all prior frames. A playback system uses this value to
+  // detect gaps in the stream, and otherwise stretch the signal to gradually
+  // re-align towards playout targets when too much drift has occurred (see
+  // `reference_time`, below).
+  RtpTimeTicks rtp_timestamp;
+
+  // The common reference clock timestamp for this frame. Over a sequence of
+  // frames, this time value is expected to drift with respect to the elapsed
+  // time implied by the RTP timestamps; and this may not necessarily increment
+  // with precise regularity.
+  //
+  // This value originates from a sender, and is the time at which the frame was
+  // captured/recorded. In the receiver context, this value is the computed
+  // target playout time, which is used for guiding the timing of presentation
+  // (see `rtp_timestamp`, above). It is also meant to be used to synchronize
+  // the presentation of multiple streams (e.g., audio and video), commonly
+  // known as "lip-sync." It is NOT meant to be a mandatory/exact playout time.
+  Clock::time_point reference_time;
+
+  // Playout delay for this and all future frames. Used by the Adaptive
+  // Playout delay extension. Non-positive values means no change.
+  std::chrono::milliseconds new_playout_delay{};
+
+  // Video capture begin/end timestamps. If set to a value other than
+  // Clock::time_point::min(), used for improved statistics gathering.
+  Clock::time_point capture_begin_time = Clock::time_point::min();
+  Clock::time_point capture_end_time = Clock::time_point::min();
+
+  // A buffer containing the encoded signal data for the frame. In the sender
+  // context, this points to the data to be sent. In the receiver context, this
+  // is set to the region of a client-provided buffer that was populated.
+  ByteView data;
+};
+
+}  // namespace openscreen::cast
+
+#endif  // CAST_STREAMING_PUBLIC_ENCODED_FRAME_H_