feat: add i18n support for Vietnamese and English

AGENTS.md

@@ -68,11 +68,19 @@ minicrm/
 │   │   │   ├── Customers/
 │   │   │   │   └── RelationManagers/FeedbacksRelationManager.php
 │   │   │   ├── FeedbackChannels/
-│   │   │   └── FeedbackTags/
+│   │   │   ├── FeedbackTags/
+│   │   │   ├── Contracts/
+│   │   │   ├── Users/
+│   │   │   └── Roles/
 │   │   └── Widgets/
 │   │       ├── ResolvedTicketsWidget.php       # Dashboard: resolved tickets table
 │   │       ├── AvgProcessingTimeWidget.php     # Dashboard: stats overview
 │   │       └── HandlerPerformanceWidget.php    # Dashboard: bar chart per handler
+│   ├── Enums/
+│   │   ├── ContractType.php
+│   │   ├── ContractStatus.php
+│   │   ├── HandoverStatus.php
+│   │   └── ServiceType.php
 │   ├── Models/
 │   │   ├── User.php                     # HasRoles (Spatie), isAdmin(), isManager()
 │   │   ├── Department.php               # NEW: name, manager_id → User
@@ -101,6 +109,15 @@ minicrm/
 │   │   └── TicketClosed.php             # DB + Mail for ticket closure
 │   └── Providers/Filament/
 │       └── AdminPanelProvider.php
+├── lang/                                # i18n translation files
+│   ├── en/
+│   │   ├── app.php                      # General UI labels, navigation, status, widgets
+│   │   ├── feedback.php                 # Feedback domain: services, notifications, interactions
+│   │   └── enums.php                    # Enum labels
+│   └── vi/
+│       ├── app.php
+│       ├── feedback.php
+│       └── enums.php
 ├── resources/views/filament/resources/feedback/
 │   ├── similar-cases.blade.php
 │   └── attachment-links.blade.php          # Modal listing attachments with signed download URLs
@@ -217,19 +234,84 @@ feedback_interactions, feedback_tags, feedback_feedback_tag, products, customers
 - AvgProcessingTimeWidget: 4 stats (resolved count, avg time, pending count, escalated count)
 - HandlerPerformanceWidget: bar chart of avg processing time per handler
 
+## Internationalization (i18n)
+
+### Configuration
+- Default locale: `vi` (Vietnamese), fallback: `en` (English)
+- Set in `.env`: `APP_LOCALE=vi`, `APP_FALLBACK_LOCALE=en`
+- Filament uses `app()->getLocale()` — no extra panel config needed
+
+### Translation Files
+```
+lang/
+├── en/
+│   ├── app.php          # General UI: navigation, labels, status, widgets, blade strings
+│   ├── feedback.php     # Feedback domain: services, notifications, interactions
+│   └── enums.php        # Enum labels (HandoverStatus, ServiceType, ContractStatus, ContractType)
+└── vi/
+    ├── app.php
+    ├── feedback.php
+    └── enums.php
+```
+
+### Translation Patterns
+```php
+// Resource labels — MUST override getPluralLabel() (not auto-translated)
+public static function getPluralLabel(): ?string
+{
+    return __('app.resource_feedbacks');
+}
+
+// Navigation group — MUST override getNavigationGroup() (not auto-translated)
+public static function getNavigationGroup(): ?string
+{
+    return __('app.nav_customer_care');
+}
+
+// Form fields — MUST add explicit ->label()
+TextInput::make('name')->label(__('app.name'))
+
+// Status options
+'options' => [
+    'pending' => __('app.status_pending'),
+    'processing' => __('app.status_processing'),
+]
+
+// Enum labels
+public function label(): string
+{
+    return match ($this) {
+        self::ACTIVE => __('enums.contract_status.active'),
+    };
+}
+
+// Widget heading/description — override getHeading()/getDescription()
+public function getHeading(): string | Htmlable | null
+{
+    return __('app.widget_avg_time_by_handler');
+}
+```
+
+### Key Gotchas
+- `$pluralLabel` property does NOT auto-translate — must override `getPluralLabel()`
+- `getNavigationGroup()` does NOT auto-translate — must call `__()` explicitly
+- `$heading`/`$description` in ChartWidget are raw properties — must override `getHeading()`/`getDescription()`
+- Form fields without `->label()` use Filament's `filament-panels::` namespace (may not resolve correctly)
+- Always add `->label(__('key'))` to TextInput, Select, Textarea, etc.
+
 ## Navigation Structure
 
 ```
 Dashboard
-├── Customer Care (group)
-│   └── Feedbacks (chat-bubble-left-right, sort=1)
-└── Management (group)
-    ├── Products (building-storefront, sort=1)
-    ├── Customers (user-group, sort=2)
-    ├── Channels (inbox-stack, sort=3)
-    ├── Tags (tag, sort=default)
-    ├── Users (users, sort=5) — admin only
-    └── Roles (shield-check, sort=6) — admin only
+├── Customer Care / Chăm sóc khách hàng (group)
+│   └── Feedbacks / Phản ánh (chat-bubble-left-right, sort=1)
+└── Management / Quản lý (group)
+    ├── Products / Sản phẩm (building-storefront, sort=1)
+    ├── Customers / Khách hàng (user-group, sort=2)
+    ├── Channels / Kênh phản ánh (inbox-stack, sort=3)
+    ├── Tags / Thẻ (tag, sort=default)
+    ├── Users / Người dùng (users, sort=5) — admin only
+    └── Roles / Vai trò (shield-check, sort=6) — admin only
 ```
 
 Dashboard widgets: ResolvedTicketsWidget, AvgProcessingTimeWidget, HandlerPerformanceWidget (admin/manager only)
@@ -337,3 +419,8 @@ $user->assignRole('manager');
 8. **ChartWidget properties**: `$heading` and `$columnSpan` are non-static in Filament's ChartWidget.
 9. **Manager closing permission**: Manager must be department head (`Department.manager_id`) to close tickets in that department.
 10. **Docker**: Entrypoint auto-generates APP_KEY and runs migrations. SQLite persists via volume mount.
+11. **i18n - pluralLabel**: `$pluralLabel` property does NOT auto-translate — must override `getPluralLabel()` and call `__()`.
+12. **i18n - navigationGroup**: `getNavigationGroup()` does NOT auto-translate — must return `__('key')` explicitly.
+13. **i18n - ChartWidget heading**: `$heading`/`$description` are raw properties — must override `getHeading()`/`getDescription()`.
+14. **i18n - form labels**: Form fields without `->label()` use Filament's `filament-panels::` namespace — always add explicit `->label(__('key'))`.
+15. **i18n - Filament vendor**: Filament ships 57 Vietnamese translation files — auto-activated when `APP_LOCALE=vi`.