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.

breadcastd/Cargo.toml

@@ -0,0 +1,24 @@
+[package]
+name = "breadcastd"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+description = "breadcast background daemon: discovery, capture/encode/serve pipeline, Cast V2 session"
+
+[[bin]]
+name = "breadcastd"
+path = "src/main.rs"
+
+[dependencies]
+breadcast-core = { path = "../breadcast-core" }
+anyhow = { workspace = true }
+serde = { workspace = true }
+tracing = { workspace = true }
+tracing-subscriber = { workspace = true }
+tokio = { workspace = true }
+serde_json = { workspace = true }
+rust_cast = { version = "0.21", features = ["thread_safe"] }
+gstreamer = "0.25"
+gstreamer-app = "0.25"
+bread-utils = { git = "https://git.breadway.dev/Breadway/bread-ecosystem", tag = "v0.7.1", features = ["bread-client"] }