refactor(log): migrate from zerolog to structured slog with bridge

- Replace direct zerolog usage with standard library `log/slog` in business code
- Add `internal/logging` package with zerolog bridge handler for structured output
- Create `internal/jsoncodec` package to centralize JSON encoding/decoding using Sonic
- Update all services and main entry point to use new logging interface
- Maintain backward compatibility with existing zerolog console output
- Remove custom logger setup in favor of structured logging bridge

internal/logging/logging.go

@@ -0,0 +1,63 @@
+package logging
+
+import (
+	"log/slog"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/rs/zerolog"
+)
+
+type Options struct {
+	Service string
+}
+
+func New(opts Options) (*slog.Logger, zerolog.Logger) {
+	level := parseLevel(strings.TrimSpace(os.Getenv("EZ_LOG_LEVEL")))
+	zerolog.SetGlobalLevel(toZerologLevel(level))
+
+	output := zerolog.ConsoleWriter{
+		Out:        os.Stdout,
+		TimeFormat: time.RFC3339,
+	}
+
+	zl := zerolog.New(output).
+		Level(toZerologLevel(level)).
+		With().
+		Timestamp().
+		Str("service", strings.TrimSpace(opts.Service)).
+		Logger()
+
+	sl := slog.New(NewZerologHandler(zl, level))
+	slog.SetDefault(sl)
+	return sl, zl
+}
+
+func parseLevel(raw string) slog.Level {
+	switch strings.ToLower(raw) {
+	case "debug":
+		return slog.LevelDebug
+	case "warn", "warning":
+		return slog.LevelWarn
+	case "error":
+		return slog.LevelError
+	case "info", "":
+		return slog.LevelInfo
+	default:
+		return slog.LevelInfo
+	}
+}
+
+func toZerologLevel(level slog.Level) zerolog.Level {
+	switch {
+	case level <= slog.LevelDebug:
+		return zerolog.DebugLevel
+	case level <= slog.LevelInfo:
+		return zerolog.InfoLevel
+	case level <= slog.LevelWarn:
+		return zerolog.WarnLevel
+	default:
+		return zerolog.ErrorLevel
+	}
+}