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.cc

@@ -0,0 +1,26 @@
+#include "patches/compat_shims.h"
+
+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) {
+  unsigned int n = *num;
+  size_t l = 0;
+  while (l < length) {
+    if (n == 0) {
+      AES_encrypt(ivec, ecount_buf, key);
+      for (int i = AES_BLOCK_SIZE - 1; i >= 0; --i) {
+        if (++ivec[i]) {
+          break;
+        }
+      }
+    }
+    out[l] = static_cast<unsigned char>(in[l] ^ ecount_buf[n]);
+    ++l;
+    n = (n + 1) % AES_BLOCK_SIZE;
+  }
+  *num = n;
+}