fix(sharednd): address review — stop/start race, onExit cleanup, no busy loop off niri

- Debounce stop transitions by 1 s (host update tick): a stop/start pair
  from switching casts collapses into no transition, so the async
  `dnd-set off` can no longer race the `dnd-status` query and drop
  ownership mid-share. Also stops DND flapping.
- Add onExit: if the plugin owns DND when disabled/reloaded, turn it off
  via a detached runAsync (survives VM teardown).
- Gate detection on NIRI_SOCKET + commandExists("niri") instead of an
  unconditional retry loop: on other compositors (or niri installed but
  not running) the service now spawns nothing. If NIRI_SOCKET is set but
  the binary is missing from PATH, warn once.
- Make the stream retry loop self-terminating (parent gone or niri
  socket removed): hard host exits skip process-group cleanup and were
  leaking orphaned loops that respawned `niri msg` every 3 s across
  sessions (observed 11 such orphans over 4 days).
- Bump version to 1.1.0.

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

sharednd/README.md

@@ -13,6 +13,9 @@ enabled. When the last screencast stops, notifications come back.
 - On every cast event it re-queries `niri msg -j casts` as the authoritative
   state, so missed or reordered events cannot desync it. The stream is wrapped
   in a shell retry loop and resends full state on reconnect.
+- Stop transitions are debounced by ~1 second: switching what is being shared
+  produces a stop/start event pair, which the debounce collapses — DND does
+  not flap, and the stop/start race cannot drop ownership.
 - DND is toggled through the host IPC (`noctalia msg notification-dnd-set`),
   so the usual OSD feedback appears.
 
@@ -35,7 +38,8 @@ enabled. When the last screencast stops, notifications come back.
 
 ## Requirements & limitations
 
-- Requires **niri** (detection is niri IPC; on other compositors the plugin
-  is inert and shows a warning at startup).
-- There is no plugin-disable hook in the host: if you disable the plugin
-  mid-share while it owns DND, DND stays on — toggle it manually.
+- Requires **niri** (detection is niri IPC). Detection only starts inside a
+  niri session (`NIRI_SOCKET` set and the `niri` binary in `PATH`); on other
+  compositors the service is inert and spawns no processes.
+- Disabling or reloading the plugin mid-share while it owns DND turns DND
+  back off (`onExit` cleanup).