docs: document login smoke advanced flags

docs/healthchecks.md

@@ -84,6 +84,24 @@ sudo -iu mt2.jakubkadlec.dev env METIN_LOGIN_SMOKE_PASSWORD='<password>' \
   --client-version=1215955205
 ```
 
+Useful direct flags:
+
+- `--json`
+  returns a machine-readable summary including timings and emitted events
+- `--expect-auth-failure=STATUS`
+  treats an auth failure such as `NOID` or `WRONGPWD` as a successful negative test
+- `--expect-channel-failure=STATUS`
+  treats a channel failure as a successful negative test
+
+Example negative auth test:
+
+```bash
+sudo -iu mt2.jakubkadlec.dev env METIN_LOGIN_SMOKE_PASSWORD='wrongpass' \
+  /home/mt2.jakubkadlec.dev/metin/build/server-src/bin/metin_login_smoke \
+  173.249.9.66 11000 11011 someuser --password-env=METIN_LOGIN_SMOKE_PASSWORD \
+  --expect-auth-failure=WRONGPWD --json
+```
+
 ## Security Notes
 
 This does not open a new public network surface. It is a local operational tool.