Non-public documents (internal, archived, confidential) were accessible
to unauthenticated users via direct slug/ID lookup. List and search
endpoints already filtered for visibility: 'public', but the individual
document endpoints did not. Added optionalAuth middleware and visibility
checks so non-public docs return 404 to public users while remaining
accessible to admin users.
Also adds Guardian Agents translations to village-case-study locale
files (DE, FR, MI) — 8 new keys per locale, flow step renumbered
6→7→8 with new Guardian Agents verification step at position 6.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>