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/util/bit_vector.cc

@@ -0,0 +1,34 @@
+// Copyright 2026 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "util/bit_vector.h"
+
+#include <algorithm>
+
+namespace openscreen {
+
+BitVector::BitVector(size_t size, Fill fill) {
+  Resize(size, fill);
+}
+
+void BitVector::Resize(size_t size, Fill fill) {
+  size_ = size;
+  v_.assign((size + kBitsPerWord - 1) / kBitsPerWord,
+            fill ? ~uint64_t{0} : uint64_t{0});
+  if (fill && size % kBitsPerWord != 0) {
+    v_.back() &= (uint64_t{1} << (size % kBitsPerWord)) - 1;
+  }
+}
+
+size_t BitVector::FindFirstSet() const {
+  for (size_t i = 0; i < v_.size(); ++i) {
+    if (v_[i] != 0) {
+      size_t pos = i * kBitsPerWord + std::countr_zero(v_[i]);
+      return (pos < size_) ? pos : size_;
+    }
+  }
+  return size_;
+}
+
+}  // namespace openscreen