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/discord/adapter.go

@@ -1,6 +1,6 @@
 package discord
 import (
-	"fmt"
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/logger"
 	"git.yeij.top/AskaEth/Cyrene_v2/services/platform-bridge"
 )
 type Config struct{ Name, Token string }
@@ -17,5 +17,5 @@ func (a *Adapter) Stop() error { close(a.done); return nil }
 func (a *Adapter) Incoming() <-chan *bridge.UnifiedMessage { return a.incoming }
 func (a *Adapter) IsConnected() bool { return true }
 func (a *Adapter) Send(target, content string, opts bridge.SendOptions) error {
-	fmt.Printf("[dc:%s] -> %s: %s\n", a.cfg.Name, target, content); return nil
+	logger.Infof("[dc:%s] -> %s: %s\n", a.cfg.Name, target, content); return nil
 }