feat: add announcement feature with admin management and home page display

backend/internal/models/announcement.go

@@ -0,0 +1,22 @@
+package models
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+)
+
+type Announcement struct {
+	ID        uint           `gorm:"primaryKey" json:"id"`
+	Title     string         `gorm:"size:255;not null" json:"title"`
+	Content   string         `gorm:"type:text" json:"content"`
+	SortOrder int            `gorm:"default:0" json:"sort_order"`
+	IsActive  bool           `gorm:"default:true" json:"is_active"`
+	CreatedAt time.Time      `json:"created_at"`
+	UpdatedAt time.Time      `json:"updated_at"`
+	DeletedAt gorm.DeletedAt `gorm:"index" json:"-"`
+}
+
+func (Announcement) TableName() string {
+	return "announcements"
+}