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/patches/compat_shims.h

@@ -0,0 +1,35 @@
+// Force-included (via -include, see ../build.rs) into every translation
+// unit in this vendored openscreen subset. Papers over a few places where
+// upstream code either relies on a BoringSSL-only API that system OpenSSL
+// doesn't expose, or was written assuming an include that some other header
+// in a full Chromium checkout happens to pull in transitively. Not part of
+// upstream openscreen -- see ../PATCHES.md.
+#ifndef PATCHES_COMPAT_SHIMS_H_
+#define PATCHES_COMPAT_SHIMS_H_
+
+// cast/streaming/impl/frame_crypto.cc uses strlen-family functions without
+// including <cstring> itself.
+#include <cstring>
+
+#include <openssl/aes.h>
+
+// CRYPTO_library_init() was an OpenSSL 1.0.x-era macro/no-op that BoringSSL
+// still defines for source compatibility; system OpenSSL 3.x has no such
+// symbol (initialization there is automatic). frame_crypto.cc's call to it
+// is a no-op on any OpenSSL version this new, so it's shimmed out entirely.
+#define CRYPTO_library_init() ((void)0)
+
+// AES_ctr128_encrypt() is a BoringSSL convenience wrapper around AES-CTR
+// that system OpenSSL's public headers don't expose. Implemented in
+// compat_shims.cc using the standard CTR-mode algorithm (NIST SP 800-38A,
+// big-endian 128-bit counter block) over AES_encrypt(), which OpenSSL does
+// still expose.
+extern "C" void AES_ctr128_encrypt(const unsigned char* in,
+                                   unsigned char* out,
+                                   size_t length,
+                                   const AES_KEY* key,
+                                   unsigned char ivec[AES_BLOCK_SIZE],
+                                   unsigned char ecount_buf[AES_BLOCK_SIZE],
+                                   unsigned int* num);
+
+#endif  // PATCHES_COMPAT_SHIMS_H_