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/apps/admin/logs/utils.go

@@ -13,6 +13,7 @@ import (
 	"github.com/gorilla/websocket"
 
 	"github.com/Rain-kl/Wavelet/internal/model"
+	"github.com/Rain-kl/Wavelet/internal/repository"
 )
 
 // getUpgrader 返回 WebSocket 升级器并执行 Origin 安全检查以防止 CSWSH 攻击
@@ -32,8 +33,7 @@ func getUpgrader() *websocket.Upgrader {
 
 			// 2. 检查配置的允许跨域 Origin (Check allowed origins in system config)
 			ctx := r.Context()
-			var sc model.SystemConfig
-			if err := sc.GetByKey(ctx, model.ConfigKeyServerAddress); err == nil && sc.Value != "" {
+			if sc, err := repository.GetSystemConfigByKey(ctx, model.ConfigKeyServerAddress); err == nil && sc.Value != "" {
 				originToCheck := strings.TrimRight(strings.TrimSpace(origin), "/")
 				allowedOrigins := strings.Split(sc.Value, ",")
 				for _, allowed := range allowedOrigins {