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/README.md

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+[![Docs](https://docs.rs/rust_cast/badge.svg)](https://docs.rs/crate/rust_cast/)
+![Build Status](https://github.com/azasypkin/rust-cast/actions/workflows/ci.yml/badge.svg)
+
+# Usage
+* [Documentation](https://docs.rs/crate/rust_cast/)
+* Try out [Rust Caster](./examples/rust_caster.rs) example to see this crate in action!
+
+# Build
+
+Proto files are taken from [Chromium Open Screen GitHub mirror](https://chromium.googlesource.com/openscreen/+/37a17677e5ded963fc41a3d8dee7a59484e5ec13/cast/common/channel/proto).
+
+By default `cargo build` won't try to generate Rust code from the files located at `protobuf/*`, if you want to do that
+use `GENERATE_PROTO` environment variable during build and make sure you have `protoc` binary in `$PATH`:
+
+```bash
+$ GENERATE_PROTO=true cargo build
+```
+
+# Run example
+
+## Generic features
+
+First, you need to figure out the address of the device to connect to. For example, you can use `avahi` with the following command:
+```bash
+$ avahi-browse -a --resolve
+```
+
+```bash
+// Get some info about the Google Cast enabled device (e.g. Chromecast). 
+$ cargo run --example rust_caster -- -a 192.168.0.100 -i
+
+Number of apps run: 1
+App#0: Default Media Receiver (CC1AD845)
+Volume level: 1
+Muted: false
+
+// Run specific app on the Chromecast.
+$ cargo run --example rust_caster -- -a 192.168.0.100 -r youtube
+
+// Stop specific active app.
+$ cargo run --example rust_caster -- -a 192.168.0.100 -s youtube
+
+// Stop currently active app.
+$ cargo run --example rust_caster -- -a 192.168.0.100 --stop-current
+
+The following app has been stopped: Default Media Receiver (CC1AD845)
+```
+
+## Media features
+```bash
+// Stream a video.
+$ cargo run --example rust_caster -- -a 192.168.0.100 -m http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4
+
+// Stream a video of specific format with buffering.
+$ cargo run --example rust_caster -- -a 192.168.0.100 -m http://xxx.webm --media-type video/webm --media-stream-type buffered
+
+// Stream video from YouTube (doesn't work with the latest YouTube app, fix is welcome).
+$ cargo run --example rust_caster -- -a 192.168.0.100 -m 7LcUOEP7Brc --media-app youtube
+
+// Display an image.
+$ cargo run --example rust_caster -- -a 192.168.0.100 -m https://azasypkin.github.io/style-my-image/images/mozilla.jpg
+
+// Change volume level.
+$ cargo run --example rust_caster -- -a 192.168.0.100 --media-volume 0.5
+
+// Mute/unmute media.
+$ cargo run --example rust_caster -- -a 192.168.0.100 --media-mute [--media-unmute]
+
+// Pause media.
+$ cargo run --example rust_caster -- -a 192.168.0.100 --media-app youtube --media-pause
+
+// Resume/play media.
+$ cargo run --example rust_caster -- -a 192.168.0.100 --media-app youtube --media-play
+
+// Seek media.
+$ cargo run --example rust_caster -- -a 192.168.0.100 --media-app youtube --media-seek 100
+```
+
+For all possible values of `--media-type` see [Supported Media for Google Cast](https://developers.google.com/cast/docs/media).
+
+# DNS TXT Record description
+
+* `md` - Model Name (e.g. "Chromecast");
+* `id` - UUID without hyphens of the particular device (e.g. xx12x3x456xx789xx01xx234x56789x0);
+* `fn` - Friendly Name of the device (e.g. "Living Room"); 
+* `rs` - Unknown (recent share???) (e.g. "Youtube TV");
+* `bs` - Uknonwn (e.g. "XX1XXX2X3456");
+* `st` - Unknown (e.g. "1");
+* `ca` - Unknown (e.g. "1234");
+* `ic` - Icon path (e.g. "/setup/icon.png");
+* `ve` - Version (e.g. "04").
+
+# Model names
+
+* `Chromecast` - Regular chromecast, supports video/audio;
+* `Chromecast Audio` - Chromecast Audio device, supports only audio.
+
+# Useful links and sources of inspiration
+
+* [DIAL Protocol](http://www.dial-multiscreen.org/);
+* [An implementation of the Chromecast CASTV2 protocol in JS](https://github.com/thibauts/node-castv2);
+* [Chromecast - steps closer to a python native api](http://www.clift.org/fred/chromecast-steps-closer-to-a-python-native-api.html);