feat: Add multi-language support (i18n)

Languages supported (8):
- English (en)
- 日本語 (ja)
- Deutsch (de)
- Français (fr)
- Español (es)
- 简体中文 (zh-CN)
- 繁體中文 (zh-TW)
- 한국어 (ko)

Changes:
- Add locale column to users table
- Add SetLocale middleware for automatic locale detection
- Add LocaleController for language switching
- Create language files with translations for all UI elements
- Add language selector to user profile page
- Update all Blade views to use translation strings

src/resources/views/livewire/document-viewer.blade.php

@@ -14,7 +14,7 @@ class="inline-flex items-center px-4 py-2 bg-indigo-600 text-white text-sm font-
                     <svg class="w-4 h-4 mr-2" fill="none" stroke="currentColor" viewBox="0 0 24 24">
                         <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M11 5H6a2 2 0 00-2 2v11a2 2 0 002 2h11a2 2 0 002-2v-5m-1.414-9.414a2 2 0 112.828 2.828L11.828 15H9v-2.828l8.586-8.586z"></path>
                     </svg>
-                    Edit
+                    {{ __('messages.documents.edit') }}
                 </a>
             @endauth
         </div>
@@ -22,12 +22,12 @@ class="inline-flex items-center px-4 py-2 bg-indigo-600 text-white text-sm font-
         <div class="flex items-center text-sm text-gray-500 space-x-4">
             @if($document->created_by)
                 <span>
-                    Created by {{ $document->creator->name }}
+                    {{ __('messages.documents.created_by') }} {{ $document->creator->name }}
                 </span>
             @endif
 
             <span>
-                Updated {{ $document->updated_at->diffForHumans() }}
+                {{ __('messages.documents.updated') }} {{ $document->updated_at->diffForHumans() }}
             </span>
         </div>
     </div>
@@ -41,7 +41,7 @@ class="inline-flex items-center px-4 py-2 bg-indigo-600 text-white text-sm font-
     @if(count($backlinks) > 0)
         <div class="border-t border-gray-200 pt-8">
             <h2 class="text-xl font-semibold text-gray-900 mb-4">
-                Linked References
+                {{ __('messages.documents.linked_references') }}
             </h2>
 
             <div class="space-y-3">
@@ -69,11 +69,11 @@ class="block p-4 bg-gray-50 rounded-lg hover:bg-gray-100 transition"
     <div class="mt-12 pt-8 border-t border-gray-200">
         <div class="grid grid-cols-2 gap-4 text-sm text-gray-500">
             <div>
-                <span class="font-medium">Path:</span>
+                <span class="font-medium">{{ __('messages.documents.path') }}:</span>
                 <code class="ml-2 text-xs bg-gray-100 px-2 py-1 rounded">{{ $document->path }}</code>
             </div>
             <div>
-                <span class="font-medium">Last modified:</span>
+                <span class="font-medium">{{ __('messages.documents.last_modified') }}:</span>
                 <span class="ml-2">{{ $document->updated_at->format('Y-m-d H:i:s') }}</span>
             </div>
         </div>