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.

contrib/hyprland.conf

@@ -0,0 +1,18 @@
+# breadcast — add these to your hyprland.conf
+#
+# This is classic hyprlang (.conf) syntax, for stock Hyprland installs. On
+# BOS specifically, hyprland.conf is deprecated in favor of a Lua config
+# (hyprland.lua) driven by JSON files (binds.json, etc.) — see
+# contrib/binds.json for the equivalent BOS-native keybind snippet instead
+# of this file. There is currently no BOS-native equivalent for the
+# layerrule lines below (no layer-rule JSON schema exists yet); on BOS the
+# popup will work without the frosted-glass blur until that's added.
+#
+# Blur: blurs what's behind the transparent window, giving the frosted-glass look.
+# ignorezero: skips blurring fully-transparent pixels (outside the panel) for
+# a cleaner result.
+layerrule = blur, breadcast
+layerrule = ignorezero, breadcast
+
+# Keybind: Super+C opens the device picker popup.
+bind = $mainMod, C, exec, breadcast