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/impl/time.cc

@@ -0,0 +1,49 @@
+// 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.
+
+#include "platform/api/time.h"
+
+#include <chrono>
+#include <ctime>
+#include <ratio>
+
+#include "util/chrono_helpers.h"
+#include "util/osp_logging.h"
+
+using std::chrono::high_resolution_clock;
+using std::chrono::steady_clock;
+using std::chrono::system_clock;
+
+namespace openscreen {
+
+Clock::time_point Clock::now() noexcept {
+  constexpr bool kSteadyIsGoodEnough =
+      std::ratio_less_equal_v<steady_clock::period, Clock::kRequiredResolution>;
+  constexpr bool kHighResIsGoodEnough =
+      std::ratio_less_equal_v<high_resolution_clock::period,
+                              Clock::kRequiredResolution> &&
+      high_resolution_clock::is_steady;
+  static_assert(kSteadyIsGoodEnough || kHighResIsGoodEnough,
+                "No suitable default clock (steady + high enough resolution) "
+                "on this platform");
+
+  // 'if constexpr' guarantees compile-time branching.
+  // We prefer steady_clock if it meets the requirements (usually cheaper).
+  if constexpr (kSteadyIsGoodEnough) {
+    return Clock::time_point(
+        Clock::to_duration(steady_clock::now().time_since_epoch()));
+  } else {
+    return Clock::time_point(
+        Clock::to_duration(high_resolution_clock::now().time_since_epoch()));
+  }
+}
+
+std::chrono::seconds GetWallTimeSinceUnixEpoch() noexcept {
+  // C++20 guarantees that system_clock uses the Unix Epoch (1970-01-01).
+  // Use floor to truncate sub-second precision safely.
+  return std::chrono::floor<std::chrono::seconds>(
+      std::chrono::system_clock::now().time_since_epoch());
+}
+
+}  // namespace openscreen