add file-based env variables for LibreTranslate and Stalwart Impersonation & handle file-based vars from JSON configs in ConfigManager

[Cameo007]

Summary

I think the missing file-based env vars are clear.
For ConfigManager however I noticed that Bulwark complains about SESSION_SECRET not being set when logging in as admin when using sessionSecretFile in config.json. The thing is, it doesn’t recognize this as variant of sessionSecret which this PR fixes.

I didn’t test LibreTranslate and Stalwart Impersonation.

Changes

• read file-based env vars for LibreTranslate and Stalwart Impersonation secrets
• add a fileKey field on CONFIG_ENV_MAP
• ConfigManager’s get and getAllWithSources now also try using fileKey

Related issues

Closes #

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactor / code quality improvement
• Chore / dependency update / CI change

Checklist

• I have read the Contributing Guide
• My code follows the project's code style and conventions
• I have run npm run typecheck && npm run lint and there are no errors
• The build passes (npm run build)
• I have tested my changes locally
• I have added or updated documentation if needed
• I have updated translations (locales/) if my changes affect user-facing text
• I have included screenshots or a screen recording for UI changes

Screenshots / demo

Notes for reviewers