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.

vendor/rust_cast-0.21.0/Cargo.toml

@@ -0,0 +1,41 @@
+[package]
+name = "rust_cast"
+description = "Library that allows you to communicate with Google Cast enabled devices (e.g. Chromecast)."
+documentation = "https://docs.rs/crate/rust_cast/"
+homepage = "https://github.com/azasypkin/rust-cast"
+repository = "https://github.com/azasypkin/rust-cast"
+readme = "README.md"
+license = "MIT"
+keywords = ["cast", "chromecast", "google"]
+version = "0.21.0"
+authors = ["Aleh Zasypkin <aleh.zasypkin@gmail.com>"]
+categories = ["api-bindings", "hardware-support", "multimedia"]
+edition = "2024"
+exclude = [
+    ".github/*",
+    "examples/*",
+    "protobuf/*",
+]
+
+[dependencies]
+byteorder = "1.5"
+log = "0.4"
+protobuf = "=3.7.2"
+rustls = "0.23"
+rustls-native-certs = "0.8"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+thiserror = "2"
+
+[dev-dependencies]
+ansi_term = "0.12"
+docopt = "1"
+env_logger = "0.11"
+mdns-sd = "0.17"
+
+[build-dependencies]
+protobuf-codegen = "=3.7.2"
+
+[features]
+thread_safe = []
+cast = []