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.

README.md

@@ -0,0 +1,97 @@
+# breadcast
+
+Cast your screen to any Chromecast/Google TV, for Hyprland. It consists of
+two binaries:
+
+- **`breadcastd`** — a background daemon that discovers Cast devices on the
+  LAN and (once built — see Status) owns the screen-capture/encode/serve
+  pipeline and the live Cast V2 session.
+- **`breadcast`** — a GTK4 Layer Shell popup for picking a device and
+  starting/stopping a cast.
+
+## Status
+
+This is early: device discovery (mDNS) and the Cast V2 sender (real device
+control — connect, launch the receiver, load media) are built and validated
+against real Chromecast/Google TV hardware. The actual screen-mirroring
+pipeline (portal-based screen capture → GPU-accelerated encode → HLS →
+local HTTP server) and the GTK4 device-picker UI are not built yet.
+`breadcastd` today only does discovery and optional breadd event
+publishing; `breadcast` is a stub binary. See `CLAUDE.md`'s Status section
+for more detail.
+
+## Requirements
+
+- Rust toolchain (edition 2021)
+- GTK 4.12+ and `gtk4-layer-shell` (once the UI lands)
+- GStreamer + `gst-plugin-pipewire`, `gst-plugins-bad` (VA-API `va` plugin),
+  `gst-plugin-hlssink3` (once the capture pipeline lands)
+- Hyprland (or any Wayland compositor with Layer Shell and the
+  `xdg-desktop-portal` ScreenCast interface)
+
+## Build
+
+```sh
+git clone https://git.breadway.dev/breadway/breadcast
+cd breadcast
+cargo build --release
+```
+
+The compiled binaries are at `target/release/breadcast` and
+`target/release/breadcastd`.
+
+## Try device discovery today
+
+```sh
+cargo run -p breadcast-core --example discover
+```
+
+Prints Chromecast/Google TV devices as they appear/disappear on the LAN.
+
+## Install
+
+Copy the binaries to somewhere on your `$PATH`, e.g.:
+
+```sh
+cp target/release/breadcast target/release/breadcastd ~/.local/bin/
+```
+
+### systemd user service
+
+A unit file is provided in `contrib/`:
+
+```sh
+cp contrib/breadcastd.service ~/.config/systemd/user/
+systemctl --user daemon-reload
+systemctl --user enable --now breadcastd
+```
+
+### Hyprland keybind
+
+For stock Hyprland, add the contents of `contrib/hyprland.conf` to your
+`hyprland.conf`:
+
+```
+layerrule = blur, breadcast
+layerrule = ignorezero, breadcast
+
+bind = $mainMod, C, exec, breadcast
+```
+
+On BOS, Hyprland config is Lua+JSON-driven instead — see
+`contrib/binds.json` for the equivalent keybind entry to merge into your
+`binds.json` by hand (there's no per-app self-registration mechanism yet).
+There is currently no BOS-native equivalent for the `layerrule` blur lines.
+
+## bread event integration
+
+`breadcastd` optionally publishes into the shared bread automation fabric
+(`bread.cast.*`) when `breadd` is running, and works identically without
+it. See `EVENTS.md` for the full, honest-about-scope contract — most of the
+eventually-planned events (mirroring start/stop) aren't implemented yet,
+since the mirroring pipeline itself isn't built yet.
+
+## Theming
+
+`breadcast` will inherit its colour palette from `bread-theme`, matching
+the rest of the ecosystem, once its GTK4 UI is built.