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)

client/src/components/PlatformIcon.jsx

@@ -0,0 +1,30 @@
+import { PLATFORMS } from '../utils/api'
+
+export default function PlatformIcon({ platform, size = 16, showLabel = false, className = '' }) {
+  const p = PLATFORMS[platform]
+  if (!p) return <span className="text-[10px] text-text-tertiary capitalize">{platform}</span>
+
+  return (
+    <span className={`inline-flex items-center gap-1 ${className}`} title={p.label}>
+      <svg
+        width={size}
+        height={size}
+        viewBox="0 0 24 24"
+        fill={p.color}
+        className="shrink-0"
+      >
+        <path d={p.icon} />
+      </svg>
+      {showLabel && <span className="text-xs text-text-secondary">{p.label}</span>}
+    </span>
+  )
+}
+
+export function PlatformIcons({ platforms = [], size = 14, gap = 'gap-1', className = '' }) {
+  if (!platforms || platforms.length === 0) return null
+  return (
+    <span className={`inline-flex items-center ${gap} ${className}`}>
+      {platforms.map(p => <PlatformIcon key={p} platform={p} size={size} />)}
+    </span>
+  )
+}