feat: port legacy KNELSecretsManager (bw-* tooling, ADRs, tests) [#769]

Secret-scanned clean (placeholder values only). Bitwarden tooling is
the head start for the Vaultwarden-SoR bootstrap (#770). legacy-* trees
exempt from lint/pointer checks (historical verbatim code).

https://projects.knownelement.com/issues/769#note-4152

legacy-knelsecretsmanager/.gitignore

@@ -0,0 +1,33 @@
+# Bitwarden configuration files containing secrets
+bitwarden-config.conf
+bitwarden-config.conf.dev
+*.conf
+!*.conf.sample
+
+# Test files
+tests/test-bitwarden-config.conf
+
+# Log files
+*.log
+/tmp/*.log
+
+# Session files
+.bw-session
+
+# Generated documentation
+COMMANDS.md
+
+# Backup files
+*.bak
+*.backup
+
+# OS specific files
+.DS_Store
+Thumbs.db
+
+# Editor files
+*.swp
+*.swo
+*~
+.vscode/
+.idea/