feat: add whyoolw/sharednd — auto DND while screen sharing (niri)

Headless service that follows niri msg -j event-stream and enables
notification Do Not Disturb via the host IPC (notification-dnd-set)
while at least one screencast is active, restoring it afterwards.

Side effects: spawns a persistent shell retry loop around
`niri msg -j event-stream`, runs `niri msg -j casts` /
`niri msg version` and `noctalia msg notification-dnd-*` on demand.
No network access, no filesystem writes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

sharednd/translations/en.json

@@ -0,0 +1,9 @@
+{
+  "title": "ShareDND",
+  "settings.only_active.label": "Only active streams",
+  "settings.only_active.description": "Count only screencasts that are actively streaming. When off, any open screencast session (even one paused or showing nothing) keeps Do Not Disturb enabled.",
+  "settings.always_off_after.label": "Always disable DND after sharing",
+  "settings.always_off_after.description": "Turn Do Not Disturb off when sharing ends even if it was already enabled before sharing started. When off, DND is only disabled if this plugin enabled it.",
+  "notify.no_niri_title": "ShareDND: niri not found",
+  "notify.no_niri_body": "Screen sharing detection uses niri IPC (niri msg). The plugin will keep retrying, but it only works under niri."
+}