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/session_config.h

@@ -0,0 +1,71 @@
+// 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 CAST_STREAMING_PUBLIC_SESSION_CONFIG_H_
+#define CAST_STREAMING_PUBLIC_SESSION_CONFIG_H_
+
+#include <array>
+#include <chrono>
+#include <cstdint>
+
+#include "cast/streaming/public/constants.h"
+#include "cast/streaming/ssrc.h"
+
+namespace openscreen::cast {
+
+// Common streaming configuration, established from the OFFER/ANSWER exchange,
+// that the Sender and Receiver are both assuming.
+struct SessionConfig final {
+  SessionConfig(Ssrc sender_ssrc,
+                Ssrc receiver_ssrc,
+                int rtp_timebase,
+                int channels,
+                std::chrono::milliseconds target_playout_delay,
+                std::array<uint8_t, 16> aes_secret_key,
+                std::array<uint8_t, 16> aes_iv_mask,
+                bool is_pli_enabled = false,
+                StreamType stream_type = StreamType::kUnknown,
+                bool are_receiver_event_logs_enabled = true);
+  SessionConfig(const SessionConfig& other);
+  SessionConfig(SessionConfig&& other) noexcept;
+  SessionConfig& operator=(const SessionConfig& other);
+  SessionConfig& operator=(SessionConfig&& other) noexcept;
+  ~SessionConfig();
+
+  bool IsValid() const;
+
+  // The sender and receiver's SSRC identifiers. Note: SSRC identifiers
+  // are defined as unsigned 32 bit integers here:
+  // https://tools.ietf.org/html/rfc5576#page-5
+  Ssrc sender_ssrc = 0;
+  Ssrc receiver_ssrc = 0;
+
+  // RTP timebase: The number of RTP units advanced per second. For audio,
+  // this is the sampling rate. For video, this is 90 kHz by convention.
+  int rtp_timebase = 90000;
+
+  // Number of channels. Must be 1 for video, for audio typically 2.
+  int channels = 1;
+
+  // Initial target playout delay.
+  std::chrono::milliseconds target_playout_delay;
+
+  // The AES-128 crypto key and initialization vector.
+  std::array<uint8_t, 16> aes_secret_key{};
+  std::array<uint8_t, 16> aes_iv_mask{};
+
+  // Whether picture loss indication (PLI) should be used for this session.
+  bool is_pli_enabled = false;
+
+  // The type (e.g. audio or video) of the stream.
+  StreamType stream_type = StreamType::kUnknown;
+
+  // Whether RTCP event logs from the Receiver are enabled. These are used for
+  // generating statistics. It is recommended that this generally be true.
+  bool are_receiver_event_logs_enabled = true;
+};
+
+}  // namespace openscreen::cast
+
+#endif  // CAST_STREAMING_PUBLIC_SESSION_CONFIG_H_