refactor(api): extract repository layer and thin HTTP handlers

Introduce internal/repository for data access and cache-backed system
config reads. Move business logic into logics.go across admin push,
user, template, cache, system_config, and upload/handler packages.

Remove Gin from internal/util by relocating request-scoped helpers to
oauth/gin_context.go. Propagate request context for config lookups in
user flows. Slim model entities and delete model-level DB/cache helpers.

Wire handlers to logics/repository so targeted packages no longer call
db.DB directly. Update admin router tests to use ErrorHandlerMiddleware.

internal/repository/upload.go

@@ -0,0 +1,118 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package repository
+
+import (
+	"context"
+	"strings"
+
+	"github.com/Rain-kl/Wavelet/internal/db"
+	"github.com/Rain-kl/Wavelet/internal/model"
+	"gorm.io/gorm"
+)
+
+// UploadListFilter filters paginated upload queries.
+type UploadListFilter struct {
+	UserID    uint64
+	Keyword   string
+	Type      string
+	Extension string
+	Page      int
+	PageSize  int
+}
+
+// ListUploads returns paginated upload records matching the filter.
+func ListUploads(ctx context.Context, filter UploadListFilter) (int64, []model.Upload, error) {
+	query := db.DB(ctx).Model(&model.Upload{}).
+		Where("status != ?", model.UploadStatusDeleted)
+
+	if filter.UserID != 0 {
+		query = query.Where("user_id = ?", filter.UserID)
+	}
+	if filter.Keyword != "" {
+		query = query.Where("LOWER(file_name) LIKE ?", "%"+strings.ToLower(filter.Keyword)+"%")
+	}
+	if filter.Type != "" {
+		query = query.Where("type = ?", filter.Type)
+	}
+	if filter.Extension != "" {
+		query = query.Where("extension = ?", strings.ToLower(filter.Extension))
+	}
+
+	var total int64
+	if err := query.Count(&total).Error; err != nil {
+		return 0, nil, err
+	}
+
+	var items []model.Upload
+	offset := (filter.Page - 1) * filter.PageSize
+	if err := query.Order("created_at DESC").Offset(offset).Limit(filter.PageSize).Find(&items).Error; err != nil {
+		return 0, nil, err
+	}
+	return total, items, nil
+}
+
+// GetActiveUploadByID loads a non-deleted upload by ID.
+func GetActiveUploadByID(ctx context.Context, id uint64) (model.Upload, error) {
+	var upload model.Upload
+	if err := db.DB(ctx).Where("id = ? AND status != ?", id, model.UploadStatusDeleted).First(&upload).Error; err != nil {
+		return model.Upload{}, err
+	}
+	return upload, nil
+}
+
+// SoftDeleteUpload marks an upload as deleted.
+func SoftDeleteUpload(ctx context.Context, upload *model.Upload) error {
+	return db.DB(ctx).Model(upload).Update("status", model.UploadStatusDeleted).Error
+}
+
+// UpdateUpload applies partial field updates to an upload record.
+func UpdateUpload(ctx context.Context, upload *model.Upload, updates map[string]any) error {
+	if len(updates) == 0 {
+		return nil
+	}
+	return db.DB(ctx).Model(upload).Updates(updates).Error
+}
+
+// ListDistinctUploadTypes returns all distinct non-empty upload business types.
+func ListDistinctUploadTypes(ctx context.Context) ([]string, error) {
+	var types []string
+	if err := db.DB(ctx).Model(&model.Upload{}).
+		Where("type IS NOT NULL AND type != ''").
+		Distinct().
+		Pluck("type", &types).Error; err != nil {
+		return nil, err
+	}
+	return types, nil
+}
+
+// FindReusableUploadByHash finds an existing upload with the same hash and size.
+func FindReusableUploadByHash(ctx context.Context, hash string, size int64) (model.Upload, error) {
+	var existing model.Upload
+	err := db.DB(ctx).
+		Where("hash = ? AND file_size = ? AND status IN (?, ?)", hash, size, model.UploadStatusPending, model.UploadStatusUsed).
+		First(&existing).Error
+	return existing, err
+}
+
+// CreateUpload persists a new upload record.
+func CreateUpload(ctx context.Context, upload *model.Upload) error {
+	return db.DB(ctx).Create(upload).Error
+}
+
+// ListUploadsByIDs returns active uploads matching the given IDs.
+func ListUploadsByIDs(ctx context.Context, ids []uint64) ([]model.Upload, error) {
+	var uploads []model.Upload
+	if err := db.DB(ctx).
+		Where("id IN ? AND status IN (?, ?)", ids, model.UploadStatusPending, model.UploadStatusUsed).
+		Find(&uploads).Error; err != nil {
+		return nil, err
+	}
+	return uploads, nil
+}
+
+// UploadQuery returns a scoped GORM query for uploads.
+func UploadQuery(ctx context.Context) *gorm.DB {
+	return db.DB(ctx).Model(&model.Upload{})
+}