fix(security): keep database passwords out of every argv

MariaDB dumps and restores read the password from MYSQL_PWD, and docker exec forwards env variables by name only, so no process listing shows a password. baudolo-restore gains --db-password-stdin; --db-password still works but warns.

🎯 Fix: 96 %
💥 Break: 3 %
💸 Cost: –
⏱️ Time: –
🛡️ Security: ~100 %
🏆 Score: 93
🚦 Gate: ✅ 90/5, cost and time <= 100, security 100 %

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -174,10 +174,14 @@ baudolo-restore postgres \
   <version> \
   --container postgres \
   --db-name appdb \
-  --db-password secret \
-  --empty
+  --db-password-stdin \
+  --empty < password-file
 ```
 
+`--db-password-stdin` reads the password from stdin. The older
+`--db-password <value>` still works but warns: it is visible in the process
+list.
+
 ### Restore MariaDB / MySQL
 
 ```bash
@@ -187,8 +191,8 @@ baudolo-restore mariadb \
   <version> \
   --container mariadb \
   --db-name shopdb \
-  --db-password secret \
-  --empty
+  --db-password-stdin \
+  --empty < password-file
 ```
 
 > `baudolo` automatically detects whether `mariadb` or `mysql`