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/handler/user_handler.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"cmp"
 	"context"
 	"crypto/sha256"
 	"fmt"
@@ -129,10 +130,7 @@ func (h *UserHandler) Login(c *gin.Context) {
 		return
 	}
 
-	account := req.Account
-	if account == "" {
-		account = req.Username
-	}
+	account := cmp.Or(req.Account, req.Username)
 	if account == "" {
 		response.BadRequest(c, "username or account is required")
 		return