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, 3 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index c16c508..4e6a658 100644
--- a/Makefile
+++ b/Makefile
@@ -5,6 +5,9 @@ endif
 ifdef DTAIL_USE_PROPRIETARY
 GO_TAGS+=proprietary
 endif
+ifdef DTAIL_NO_ZSTD
+GO_TAGS+=nozstd
+endif
 all: build
 build: dserver dcat dgrep dmap dtail dtailhealth dtail-tools
 build-pgo: pgo-build-binaries