secrets: migrate exposed plaintext secrets to git-crypt

Move all hardcoded credentials out of tracked compose/env files into the
git-crypt-encrypted secrets/ directory, using each app's supported mechanism:

- env_file -> secrets/*.env: mealie, navidrome, karakeep, meilisearch,
  baserow, maloja, valheim, photoprism, komf, openldap, penpot, vaultwarden
- file:///run/secrets: authentik email password
- jelu DB password appended to existing secrets/jelu.env

Untrack root .env (interpolated ${VAR} secrets) and add sanitized
.env.example template; gitignore /.env.

Move unreferenced orphan files (mediawiki/rtorrent/snibox .env) into
secrets/ to preserve values while encrypting them.

Add SECURITY.md documenting the secrets conventions and a rotation
checklist. NOTE: all migrated values remain in prior git history and
must be rotated at their providers.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

services/jelu.yml

@@ -19,7 +19,7 @@ services:
     environment:
       SERVER_PORT: 80
       SPRING_DATASOURCE_USERNAME: lukas
-      SPRING_DATASOURCE_PASSWORD: Q^k5i2^hN!wmEr6JLkYP9ME
+      # SPRING_DATASOURCE_PASSWORD provided via secrets/jelu.env
       JELU_CORS_ALLOWED-ORIGINS: https://jelu.${DOMAIN}
     restart: unless-stopped