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/append-field/index.js

@@ -0,0 +1,12 @@
+var parsePath = require('./lib/parse-path')
+var setValue = require('./lib/set-value')
+
+function appendField (store, key, value) {
+  var steps = parsePath(key)
+
+  steps.reduce(function (context, step) {
+    return setValue(context, step, context[step.key], value)
+  }, store)
+}
+
+module.exports = appendField