HedgeDoc: Missing validation of incoming permission values on change

HedgeDoc is an open source, real-time collaborative markdown notes application. Prior to 1.11.1, the WebSocket permission handler allows a note owner to store strings outside the supported freely, editable, limited, locked, protected, and private permission values. The viewing and editing checks handle only known values and can otherwise fall through to permissive behavior, making a note readable or writable more broadly than intended. SQLite deployments can persist the invalid value because the database column does not strictly enforce the set, while MySQL and PostgreSQL reject the database update but can leave the in-memory note state inconsistent for connected users until reload or cache eviction. Exploitation requires the note owner to intentionally submit an invalid permission value, and the owner could already choose a legitimate permissive setting, which limits the practical security impact. This issue is fixed in version 1.11.1.