Screencast: cast the desktop to Cast, DLNA and AirPlay receivers

An Omarchy shell plugin: a Python/asyncio daemon that discovers network
displays and serves an encoded screen capture for them to pull, plus a
Quickshell bar widget and panel to drive it.

The screen comes from the xdg-desktop-portal ScreenCast interface (asked
for every time, never remembered), goes through GStreamer, and is served
from a local HTTP port. Desktop audio is mixed in from the default
output's monitor. The container follows the receiver: WebM/VP8 for Cast,
MPEG-TS/H.264 for DLNA, HLS for AirPlay video.

The stream port has to be reachable from the LAN, and none of these
protocols can carry a credential, so the capability is the URL: a fresh
random path per session, refused to anything off the LAN, capped at four
concurrent readers.

daemon/requirements.txt

@@ -0,0 +1,5 @@
+# Runtime dependencies of screencast-server (installed into ~/.local/lib/screencast/venv).
+aiohttp>=3.9
+zeroconf>=0.130
+pychromecast>=13
+dbus-fast>=2.21