feat: remove Vaultwarden — migrated to Passbolt

Credentials migrated to Passbolt CE at passbolt.pivoine.art.
Removed stack files and README entry. Data wiped on VPS.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -16,7 +16,6 @@ Each stack is independently deployable with its own `compose.yml` and `.env`. Al
 | `n8n` | Workflow automation & notification relay | n8n, db |
 | `gitea` | Git hosting + CI runner | gitea, runner, db |
 | `coolify` | Deployment platform | coolify, realtime, redis, db |
-| `vaultwarden` | Password manager (legacy) | vaultwarden |
 | `passbolt` | Password manager (GPG-encrypted, team sharing) | passbolt, db |
 
 ## Tools