Marketing Hub: RBAC, i18n (AR/EN), tasks overhaul, team/user merge, tutorial

Features:
- Full RBAC with 3 roles (superadmin/manager/contributor)
- Ownership tracking on posts, tasks, campaigns, projects
- Task system: assign to anyone, filter combobox, visibility scoping
- Team members merged into users table (single source of truth)
- Post thumbnails on kanban cards from attachments
- Publication link validation before publishing
- Interactive onboarding tutorial with Settings restart
- Full Arabic/English i18n with RTL layout support
- Language toggle in sidebar, IBM Plex Sans Arabic font
- Brand-based visibility filtering for non-superadmins
- Manager can only create contributors
- Profile completion flow for new users
- Cookie-based sessions (express-session + SQLite)

server/node_modules/multer/lib/multer-error.js

@@ -0,0 +1,24 @@
+var util = require('util')
+
+var errorMessages = {
+  LIMIT_PART_COUNT: 'Too many parts',
+  LIMIT_FILE_SIZE: 'File too large',
+  LIMIT_FILE_COUNT: 'Too many files',
+  LIMIT_FIELD_KEY: 'Field name too long',
+  LIMIT_FIELD_VALUE: 'Field value too long',
+  LIMIT_FIELD_COUNT: 'Too many fields',
+  LIMIT_UNEXPECTED_FILE: 'Unexpected field',
+  MISSING_FIELD_NAME: 'Field name missing'
+}
+
+function MulterError (code, field) {
+  Error.captureStackTrace(this, this.constructor)
+  this.name = this.constructor.name
+  this.message = errorMessages[code]
+  this.code = code
+  if (field) this.field = field
+}
+
+util.inherits(MulterError, Error)
+
+module.exports = MulterError