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/constants.cc

@@ -0,0 +1,57 @@
+// Copyright 2024 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/constants.h"
+
+#include <ostream>
+
+#include "util/osp_logging.h"
+
+namespace openscreen::cast {
+
+std::ostream& operator<<(std::ostream& os, VideoCodec codec) {
+  const char* str = nullptr;
+  switch (codec) {
+    case VideoCodec::kH264:
+      str = "H264";
+      break;
+    case VideoCodec::kVp8:
+      str = "VP8";
+      break;
+    case VideoCodec::kHevc:
+      str = "HEVC";
+      break;
+    case VideoCodec::kNotSpecified:
+      str = "NotSpecified";
+      break;
+    case VideoCodec::kVp9:
+      str = "VP9";
+      break;
+    case VideoCodec::kAv1:
+      str = "AV1";
+      break;
+    default:
+      OSP_NOTREACHED();
+  }
+  os << str;
+  return os;
+}
+
+std::ostream& operator<<(std::ostream& os, CastMode mode) {
+  const char* str = nullptr;
+  switch (mode) {
+    case CastMode::kMirroring:
+      str = "mirroring";
+      break;
+    case CastMode::kRemoting:
+      str = "remoting";
+      break;
+    default:
+      OSP_NOTREACHED();
+  }
+  os << str;
+  return os;
+}
+
+}  // namespace openscreen::cast