fix: daemon lifecycle cleanup and error logging improvements

- Refactor HealthDaemon to use a tracked session (AbortController + awaitable
  promise) instead of fire-and-forget health check loops, preventing health
  checks from running after a service is stopped
- Stop health checks before terminating daemon to avoid false crash reports
  during intentional shutdown
- Guard onExit callbacks with AbortSignal to prevent stale session callbacks
- Add logErrorOnce utility to deduplicate repeated error logging
- Fix SystemForEmbassy.stop() to capture clean promise before deleting ref
- Treat SIGTERM (signal 15) as successful exit in subcontainer sync
- Fix asError to return original Error instead of wrapping in new Error
- Remove unused ExtendedVersion import from Backups.ts

core/src/service/effects/subcontainer/sync.rs

@@ -768,7 +768,7 @@ pub fn exec(
         stderr_thread.map(|t| t.join().unwrap());
         if let Some(code) = exit.code() {
             std::process::exit(code);
-        } else if exit.success() {
+        } else if exit.success() || exit.signal() == Some(15) {
             Ok(())
         } else {
             Err(Error::new(