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.

bakery.toml

@@ -0,0 +1,34 @@
+name = "breadcast"
+description = "Cast your screen to any Chromecast/Google TV or DLNA renderer — daemon + GTK4 popup"
+binaries = ["breadcast", "breadcastd"]
+# gst-plugin-va: the `vah264enc` element both encode pipelines use (see
+# breadcast-core/src/pipeline/mod.rs) -- a separate Arch package from
+# gst-plugins-bad itself, not bundled into it. jsoncpp/openssl: runtime
+# shared-library deps of breadcastd itself (not just a build dep of
+# breadcast-caststream-sys), confirmed via `ldd target/release/breadcastd`
+# showing libjsoncpp.so/libcrypto.so -- the vendored openscreen Cast
+# Streaming code (see breadcast-caststream-sys/vendor/openscreen) links
+# dynamically against the system's jsoncpp/libcrypto rather than vendoring
+# them too.
+system_deps = [
+    "gtk4",
+    "gtk4-layer-shell",
+    "gstreamer",
+    "gst-plugin-pipewire",
+    "gst-plugins-bad",
+    "gst-plugin-hlssink3",
+    "gst-plugin-va",
+    "jsoncpp",
+    "openssl",
+]
+optional_system_deps = ["hyprland", "xdg-desktop-portal-hyprland"]
+bread_deps = []
+
+[[service]]
+unit = "breadcastd.service"
+enable = true
+
+[install]
+post_install = [
+    "systemctl --user is-active --quiet breadcastd || systemctl --user start breadcastd",
+]