Fix known-hosts trust deadlock, host key stat, and optional nozstd build

- stdout logger: release mutex while waiting on pause resume so prompt
  callbacks can log (fixes hang after trusting new hosts; known_hosts
  was written but Resume never ran).
- known hosts callback: stop borrowing the SSH dial throttle channel
  (could block or interact badly with parallel handshakes).
- host key path: use errors.Is(..., fs.ErrNotExist) for RootedPath.Stat
  wrapped errors; stat errors now fail fast instead of mis-read.
- public key path: same ErrNotExist check for authorized_keys miss.
- Build: optional DTAIL_NO_ZSTD=yes / nozstd tag for CGO-free builds;
  split zstd readers into tagged files.
- Docs/examples: firewalld note for port 2222, log prune timer+script,
  SSHBindAddress note, dserver unit disabled-by-default comment;
  firewalld helper script example.
- Regression test for stdout pause/mutex behavior.

Made-with: Cursor

1 files changed, 2 insertions, 0 deletions

diff --git a/examples/dserver.service.example b/examples/dserver.service.example
index c5e5e59..f299025 100644
--- a/examples/dserver.service.example
+++ b/examples/dserver.service.example
@@ -1,3 +1,5 @@
+# Installs disabled by default: do not run `systemctl enable dserver` unless you
+# want it at boot. Start manually with: sudo systemctl start dserver
 [Unit]
 Description=DTail server
 After=network.target