refactor: replace standard log with zap logger and optimize code patterns

- Migrate all log.Printf/log.Println calls to structured zap logging
- Use cmp.Or for cleaner default value handling
- Replace manual loops with slices.ContainsFunc/IndexFunc
- Add batch query methods (IsLikedBatch, IsFavoritedBatch) to solve N+1 problem
- Update JSON tags from omitempty to omitzero for numeric fields
- Use errgroup-style wg.Go for worker goroutines
- Remove duplicate casbin/v2 dependency (keeping v3)
- Add plans/ to gitignore

internal/config/config.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"cmp"
 	"fmt"
 	"os"
 	"strconv"
@@ -236,8 +237,5 @@ func Load(configPath string) (*Config, error) {
 
 // getEnvOrDefault 获取环境变量值，如果未设置则返回默认值
 func getEnvOrDefault(key, defaultValue string) string {
-	if value := os.Getenv(key); value != "" {
-		return value
-	}
-	return defaultValue
+	return cmp.Or(os.Getenv(key), defaultValue)
 }