feat: add configurable thread count for file processing

perf: add UserStorages map and implement GetUserStorages function for…

… user-specific storage retrieval

fix: add UserID to link message and enforce default storage setting i…

…n silent handler

fix: update user and file deletion to use unscoped delete; add user s…

…ynchronization logic

fix: update create user to new config

fix: update permission check

chore: update config example and docker compose file

chore: update config comment

feat: update help message to include default storage location and sil…

…ent mode details

feat: support save content protect channel message by handle link