feat(cron): add automatic log cleanup with retention policy

Implement LogCleaner cron job to automatically clean up old log records
based on configurable retention period and maximum record count.

- Add LogCleaner with retention_days and max_records configuration
- Add EZ_LOG_RETENTION_DAYS and EZ_LOG_MAX_RECORDS environment variables
- Default to 30 days retention and 1,000,000 max records
- Include unit tests for log cleaner functionality

internal/cron/log_cleaner_test.go

@@ -0,0 +1,87 @@
+package cron
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/ez-api/ez-api/internal/model"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+)
+
+func TestLogCleanerRetentionDeletesOld(t *testing.T) {
+	dsn := fmt.Sprintf("file:%s?mode=memory&cache=shared", t.Name())
+	db, err := gorm.Open(sqlite.Open(dsn), &gorm.Config{})
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	if err := db.AutoMigrate(&model.LogRecord{}); err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+
+	now := time.Now().UTC()
+	old := model.LogRecord{ModelName: "m1", StatusCode: 200}
+	old.CreatedAt = now.Add(-48 * time.Hour)
+	fresh := model.LogRecord{ModelName: "m1", StatusCode: 200}
+	fresh.CreatedAt = now.Add(-2 * time.Hour)
+
+	if err := db.Create(&old).Error; err != nil {
+		t.Fatalf("create old: %v", err)
+	}
+	if err := db.Create(&fresh).Error; err != nil {
+		t.Fatalf("create fresh: %v", err)
+	}
+
+	cleaner := NewLogCleaner(db, nil, 1, 0, time.Minute)
+	if err := cleaner.cleanOnce(context.Background()); err != nil {
+		t.Fatalf("clean once: %v", err)
+	}
+
+	var remaining int64
+	if err := db.Model(&model.LogRecord{}).Count(&remaining).Error; err != nil {
+		t.Fatalf("count logs: %v", err)
+	}
+	if remaining != 1 {
+		t.Fatalf("expected 1 log remaining, got %d", remaining)
+	}
+}
+
+func TestLogCleanerMaxRecordsKeepsLatest(t *testing.T) {
+	dsn := fmt.Sprintf("file:%s?mode=memory&cache=shared", t.Name())
+	db, err := gorm.Open(sqlite.Open(dsn), &gorm.Config{})
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	if err := db.AutoMigrate(&model.LogRecord{}); err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+
+	for i := 0; i < 5; i++ {
+		if err := db.Create(&model.LogRecord{ModelName: "m1", StatusCode: 200}).Error; err != nil {
+			t.Fatalf("create log %d: %v", i, err)
+		}
+	}
+
+	cleaner := NewLogCleaner(db, nil, 0, 3, time.Minute)
+	if err := cleaner.cleanOnce(context.Background()); err != nil {
+		t.Fatalf("clean once: %v", err)
+	}
+
+	var remaining int64
+	if err := db.Model(&model.LogRecord{}).Count(&remaining).Error; err != nil {
+		t.Fatalf("count logs: %v", err)
+	}
+	if remaining != 3 {
+		t.Fatalf("expected 3 logs remaining, got %d", remaining)
+	}
+
+	var min model.LogRecord
+	if err := db.Order("id asc").First(&min).Error; err != nil {
+		t.Fatalf("fetch min log: %v", err)
+	}
+	if min.ID < 3 {
+		t.Fatalf("expected min id >= 3, got %d", min.ID)
+	}
+}