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/binds.json

@@ -0,0 +1,6 @@
+{
+  "_comment": "BOS-native keybind snippet (hyprland.lua + JSON config, not classic hyprland.conf — see CONTRIBUTING.md/README for context). There is no per-app self-registration mechanism today: merge this entry's contents into the 'bindings' array of BOS's own skel binds.json by hand, the same way breadclip's Super+V entry was added. Not auto-installed by bakery.",
+  "bindings": [
+    { "action": "exec", "command": "breadcast", "key": "C", "label": "Cast your screen (breadcast)", "category": "apps", "demo_cmd": "breadcast" }
+  ]
+}

contrib/breadcastd.service

@@ -0,0 +1,19 @@
+[Unit]
+Description=breadcast screen-mirroring daemon
+Documentation=https://git.breadway.dev/breadway/breadcast
+# Start after the graphical session is ready so WAYLAND_DISPLAY is set
+After=graphical-session.target
+PartOf=graphical-session.target
+
+[Service]
+Type=simple
+ExecStart=%h/.cargo/bin/breadcastd
+Restart=on-failure
+RestartSec=2
+
+# Forward stdout/stderr to the journal so `journalctl --user -u breadcastd` works
+StandardOutput=journal
+StandardError=journal
+
+[Install]
+WantedBy=graphical-session.target

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