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.

manifest.json

@@ -0,0 +1,36 @@
+{
+  "schemaVersion": 1,
+  "id": "io.github.alanfortlink.screencast",
+  "name": "Screencast",
+  "version": "0.1.0",
+  "author": "alanfortlink",
+  "license": "MIT",
+  "description": "Find the displays on your network — Google Cast, AirPlay and DLNA — and cast this desktop to them, with volume, pause and stop from the bar.",
+  "kinds": [
+    "service",
+    "bar-widget"
+  ],
+  "keepLoaded": true,
+  "entryPoints": {
+    "service": "plugin/Service.qml",
+    "barWidget": "plugin/Panel.qml"
+  },
+  "barWidget": {
+    "displayName": "Screencast",
+    "description": "Cast the screen to a TV, Chromecast or speaker on the network; the icon lights up while casting.",
+    "category": "Media",
+    "allowMultiple": false,
+    "defaultSection": "right",
+    "defaults": {
+      "alwaysShow": true
+    },
+    "schema": [
+      {
+        "key": "alwaysShow",
+        "type": "boolean",
+        "label": "Show the icon even when nothing is being cast",
+        "defaultValue": true
+      }
+    ]
+  }
+}