Align POS header with other apps: AI assistant, register button, sidebar

- Add the Afia AI assistant to the header (topbar AI button + slide-over),
  matching every other Ladill app. Ports config/afia.php, AfiaService, a POS
  AiController (pos.ai.chat) scoped to register/sales/products, and includes
  the slide-over in the app layout. The afia() Alpine component already existed.
- Hide the header "Open register" button while on the register page.
- Move Settings to a pinned bottom section of the sidebar, like other apps.
- Commit the updated POS logo + launcher icon assets.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

config/afia.php

@@ -0,0 +1,11 @@
+<?php
+
+return [
+    // Afia — Ladill in-app AI assistant, scoped to POS. Provisioned per app via
+    // its own key (falls back to OPENAI_API_KEY). See App\Services\Afia\AfiaService.
+    'product' => env('AFIA_PRODUCT', 'pos'),
+    'enabled' => (bool) env('AFIA_ENABLED', true),
+    'provider' => env('AFIA_PROVIDER', 'openai'), // openai | anthropic
+    'model' => env('AFIA_MODEL', 'gpt-4o-mini'),
+    'api_key' => env('AFIA_API_KEY', env('OPENAI_API_KEY')),
+];