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/impl/frame_crypto.cc

@@ -0,0 +1,106 @@
+// 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/impl/frame_crypto.h"
+
+#include <random>
+#include <utility>
+
+#include "openssl/crypto.h"
+#include "openssl/err.h"
+#include "openssl/rand.h"
+#include "platform/base/span.h"
+#include "util/big_endian.h"
+#include "util/crypto/openssl_util.h"
+#include "util/crypto/random_bytes.h"
+#include "util/osp_logging.h"
+
+namespace openscreen::cast {
+
+EncryptedFrame::EncryptedFrame() {
+  data = owned_data_;
+}
+
+EncryptedFrame::~EncryptedFrame() = default;
+
+EncryptedFrame::EncryptedFrame(EncryptedFrame&& other) noexcept
+    : EncodedFrame(static_cast<EncodedFrame&&>(other)),
+      owned_data_(std::move(other.owned_data_)) {
+  data = owned_data_;
+  other.data = ByteView();
+}
+
+EncryptedFrame& EncryptedFrame::operator=(EncryptedFrame&& other) {
+  this->EncodedFrame::operator=(static_cast<EncodedFrame&&>(other));
+  owned_data_ = std::move(other.owned_data_);
+  data = owned_data_;
+  other.data = ByteView();
+  return *this;
+}
+
+FrameCrypto::FrameCrypto(const std::array<uint8_t, 16>& aes_key,
+                         const std::array<uint8_t, 16>& cast_iv_mask)
+    : aes_key_{}, cast_iv_mask_(cast_iv_mask) {
+  // Ensure that the library has been initialized. CRYPTO_library_init() may be
+  // safely called multiple times during the life of a process.
+  CRYPTO_library_init();
+
+  // Initialize the 244-byte AES_KEY struct once, here at construction time. The
+  // const_cast<> is reasonable as this is a one-time-ctor-initialized value
+  // that will remain constant from here onward.
+  const int return_code = AES_set_encrypt_key(
+      aes_key.data(), aes_key.size() * 8, const_cast<AES_KEY*>(&aes_key_));
+  if (return_code != 0) {
+    ClearOpenSSLERRStack(CURRENT_LOCATION);
+    OSP_LOG_FATAL << "Failure when setting encryption key; unsafe to continue.";
+    OSP_NOTREACHED();
+  }
+}
+
+FrameCrypto::~FrameCrypto() = default;
+
+EncryptedFrame FrameCrypto::Encrypt(const EncodedFrame& encoded_frame) const {
+  EncryptedFrame result;
+  encoded_frame.CopyMetadataTo(&result);
+  result.owned_data_.resize(encoded_frame.data.size());
+  result.data = result.owned_data_;
+  Crypt(encoded_frame.frame_id, {&encoded_frame.data, 1}, result.owned_data_);
+  return result;
+}
+
+void FrameCrypto::Decrypt(FrameId frame_id,
+                          ChunkList chunks,
+                          ByteBuffer out) const {
+  Crypt(frame_id, chunks, out);
+}
+
+void FrameCrypto::Crypt(FrameId frame_id,
+                        ChunkList chunks,
+                        ByteBuffer out) const {
+  OSP_CHECK(!frame_id.is_null());
+
+  // Compute the AES nonce for Cast Streaming payload encryption, which is based
+  // on the `frame_id`.
+  std::array<uint8_t, 16> aes_nonce{};
+  static_assert(AES_BLOCK_SIZE == sizeof(aes_nonce),
+                "AES_BLOCK_SIZE is not 16 bytes.");
+  WriteBigEndian<uint32_t>(frame_id.lower_32_bits(), aes_nonce.data() + 8);
+  for (size_t i = 0; i < aes_nonce.size(); ++i) {
+    aes_nonce[i] ^= cast_iv_mask_[i];
+  }
+
+  std::array<uint8_t, 16> ecount_buf{};
+  unsigned int block_offset = 0;
+  size_t out_offset = 0;
+  for (ByteView chunk : chunks) {
+    OSP_CHECK_LE(out_offset + chunk.size(), out.size());
+    AES_ctr128_encrypt(chunk.data(), out.data() + out_offset, chunk.size(),
+                       &aes_key_, aes_nonce.data(), ecount_buf.data(),
+                       &block_offset);
+    out_offset += chunk.size();
+  }
+  OSP_CHECK_EQ(out_offset, out.size());
+}
+
+}  // namespace openscreen::cast