refactor(logging): replace all print/log with structured slog logger

- main.go: 30+ log.Printf → logger.Infof
- plugin/registry: 12 log.Printf → logger.Infof
- db/db.go, ws/hub.go: log → logger
- platform-bridge: fmt.Printf/println → logger.Info
- Logs now: time=... level=INFO msg=...
- 16 packages pass, vet clean

backend/services/platform-bridge/bridge.go

@@ -2,7 +2,11 @@
 // It defines unified message types and adapter interfaces for QQ, Telegram, Discord, and Webhook.
 package bridge
 
-import "time"
+import (
+	"time"
+
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/logger"
+)
 
 // UnifiedMessage is the internal representation of a message from any platform.
 type UnifiedMessage struct {
@@ -85,7 +89,7 @@ func (r *Router) StartAll() {
 	for name, a := range r.adapters {
 		go func(name string, a Adapter) {
 			if err := a.Start(); err != nil {
-				println("[bridge]", name, "start error:", err.Error())
+				logger.Info("[bridge]", name, "start error:", err.Error())
 				return
 			}
 			for msg := range a.Incoming() {