Add audit log for moderation and admin actions

New audit_log table records actor, action, target and a JSON snapshot
of the details, so entries stay readable after the target is deleted;
the actor is set to NULL when the user is removed. logAudit() is called
from upload delete (single and bulk), comment delete, tag removal, role
create/delete, role permission changes, role assign/revoke and MOTD
updates. Logging failures only warn and never fail the action itself.

The admin page gets an audit card behind the new audit.view permission
with action filter, click-to-filter by user, readable summaries per
action and server-side pagination. Action catalog lives in
shared/utils/audit.ts, labels under admin.auditActions (de/en).

Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

shared/utils/permissions.ts

@@ -6,6 +6,7 @@ export const PERMISSIONS = [
   { key: 'comment.delete', label: 'Kommentare löschen' },
   { key: 'upload.delete', label: 'Uploads löschen' },
   { key: 'tag.delete', label: 'Tags löschen' },
+  { key: 'audit.view', label: 'Audit-Log einsehen' },
 ] as const
 
 export type PermissionKey = (typeof PERMISSIONS)[number]['key']