feat(server): implement chat file TTL cleanup and enhance JPush vendor channel support

Add FileCleanupWorker for automatic expiration of chat files with configurable retention period and batch processing. Files uploaded via `/api/v1/uploads/files` are tracked in `uploaded_files` table with expiration timestamps, then deleted from S3 and database upon expiry. Expired file URLs are injected as `"expired": true` in message responses.

Extend JPush push notification configuration with vendor-specific channel_id support (xiaomi, huawei, oppo, vivo, meizu, honor, fcm) for differentiating system vs chat notifications. Add iOS APNs thread-id grouping configuration for notification categorization.

internal/model/uploaded_file.go

@@ -0,0 +1,26 @@
+package model
+
+import "time"
+
+// UploadedFile 聊天/通用文件上传记录
+// 用于跟踪 files/ 前缀下的 S3 对象，配合 FileCleanupWorker 实现 TTL 过期清理。
+// 注意：images/avatars/covers 等内容寻址资源不记录本表，不会被自动清理。
+type UploadedFile struct {
+	ID         uint       `gorm:"primaryKey;autoIncrement" json:"id"`
+	URL        string     `gorm:"size:512;index;not null" json:"url"`        // 完整访问 URL，DTO 标记失效用
+	ObjectName string     `gorm:"size:256;index;not null" json:"object_name"` // S3 对象名 files/{folder}/{hash}{ext}
+	Name       string     `gorm:"size:255" json:"name"`                       // 原始文件名
+	Size       int64      `json:"size"`                                       // 字节数
+	MimeType   string     `gorm:"size:128" json:"mime_type"`
+	Folder     string     `gorm:"size:32;index" json:"folder"`                // chat / post 等来源
+	UploaderID string     `gorm:"size:50;index" json:"uploader_id"`           // 上传者 UUID
+	Expired    bool       `gorm:"index;default:false" json:"expired"`         // 是否已从 S3 清理
+	ExpiredAt  *time.Time `json:"expired_at,omitempty"`                       // 清理时间
+	CreatedAt  time.Time  `gorm:"index" json:"created_at"`                    // 上传时间，TTL 计算基准
+	UpdatedAt  time.Time  `json:"updated_at"`
+}
+
+// TableName 表名
+func (UploadedFile) TableName() string {
+	return "uploaded_files"
+}