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/model/init.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"time"
 
+	"go.uber.org/zap"
 	"gorm.io/driver/postgres"
 	"gorm.io/driver/sqlite"
 	"gorm.io/gorm"
@@ -67,7 +68,9 @@ func NewDB(cfg *config.DatabaseConfig) (*gorm.DB, error) {
 		return nil, fmt.Errorf("failed to auto migrate: %w", err)
 	}
 
-	log.Printf("Database connected (%s) and migrated successfully", cfg.Type)
+	zap.L().Info("Database connected and migrated successfully",
+		zap.String("type", cfg.Type),
+	)
 	return db, nil
 }
 
@@ -220,7 +223,9 @@ func seedRoles(db *gorm.DB) error {
 		return err
 	}
 
-	log.Printf("Seeded %d roles successfully", len(roles))
+	zap.L().Info("Seeded roles successfully",
+		zap.Int("count", len(roles)),
+	)
 	return nil
 }
 
@@ -276,7 +281,9 @@ func seedPermissions(db *gorm.DB) error {
 		return err
 	}
 
-	log.Printf("Seeded %d permissions successfully", len(permissions))
+	zap.L().Info("Seeded permissions successfully",
+		zap.Int("count", len(permissions)),
+	)
 	return nil
 }