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.cc

@@ -0,0 +1,54 @@
+// 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.
+
+#include "cast/streaming/public/session_config.h"
+
+#include <algorithm>
+#include <utility>
+
+namespace openscreen::cast {
+
+namespace {
+
+bool IsNonZero(uint8_t byte) {
+  return byte > 0;
+}
+
+}  // namespace
+
+SessionConfig::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,
+                             StreamType stream_type,
+                             bool are_receiver_event_logs_enabled)
+    : sender_ssrc(sender_ssrc),
+      receiver_ssrc(receiver_ssrc),
+      rtp_timebase(rtp_timebase),
+      channels(channels),
+      target_playout_delay(target_playout_delay),
+      aes_secret_key(std::move(aes_secret_key)),
+      aes_iv_mask(std::move(aes_iv_mask)),
+      is_pli_enabled(is_pli_enabled),
+      stream_type(stream_type),
+      are_receiver_event_logs_enabled(are_receiver_event_logs_enabled) {}
+
+SessionConfig::SessionConfig(const SessionConfig& other) = default;
+SessionConfig::SessionConfig(SessionConfig&& other) noexcept = default;
+SessionConfig& SessionConfig::operator=(const SessionConfig& other) = default;
+SessionConfig& SessionConfig::operator=(SessionConfig&& other) noexcept =
+    default;
+SessionConfig::~SessionConfig() = default;
+
+bool SessionConfig::IsValid() const {
+  return sender_ssrc > 0 && receiver_ssrc > 0 && rtp_timebase > 0 &&
+         channels > 0 &&
+         std::any_of(aes_secret_key.begin(), aes_secret_key.end(), IsNonZero) &&
+         std::any_of(aes_iv_mask.begin(), aes_iv_mask.end(), IsNonZero);
+}
+}  // namespace openscreen::cast