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/platform/api/logging.h

@@ -0,0 +1,62 @@
+// Copyright 2018 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef PLATFORM_API_LOGGING_H_
+#define PLATFORM_API_LOGGING_H_
+
+#include <sstream>
+
+namespace openscreen {
+
+enum class LogLevel {
+  // Very detailed information, often used for evaluating performance or
+  // debugging production issues in-the-wild.
+  kVerbose = 0,
+
+  // Used occasionally to note events of interest, but not for indicating any
+  // problems. This is also used for general console messaging in Open Screen's
+  // standalone executables.
+  kInfo = 1,
+
+  // Indicates a problem that may or may not lead to an operational failure.
+  kWarning = 2,
+
+  // Indicates an operational failure that may or may not cause a component to
+  // stop working.
+  kError = 3,
+
+  // Indicates a logic flaw, corruption, impossible/unanticipated situation, or
+  // operational failure so serious that Open Screen will soon call Break() to
+  // abort the current process. Examples: security/privacy risks, memory
+  // management issues, API contract violations.
+  kFatal = 4,
+};
+
+// Returns true if `level` is at or above the level where the embedder will
+// record/emit log entries from the code in `file`.
+bool IsLoggingOn(LogLevel level, const std::string_view file);
+
+// Record a log entry, consisting of its logging level, location and message.
+// The embedder may filter-out entries according to its own policy, but this
+// function will not be called if IsLoggingOn(level, file) returns false.
+// Whenever `level` is kFatal, Open Screen will call Break() immediately after
+// this returns.
+//
+// `message` is passed as a string stream to avoid unnecessary string copies.
+// Embedders can call its rdbuf() or str() methods to access the log message.
+void LogWithLevel(LogLevel level,
+                  const char* file,
+                  int line,
+                  std::stringstream message);
+
+// Breaks into the debugger, if one is present. Otherwise, aborts the current
+// process (i.e., this function should not return). In production builds, an
+// embedder could invoke its infrastructure for performing "dumps," consisting
+// of thread stack traces and other relevant process state information, before
+// aborting the process.
+[[noreturn]] void Break();
+
+}  // namespace openscreen
+
+#endif  // PLATFORM_API_LOGGING_H_