fix: address code review findings

- Fix type mismatch in search_cache.go: SearchWithCache now returns *yandex.Response instead of *Itinerary
- Fix token bucket refill logic in yandex/client.go to properly accumulate tokens based on refillPerSec
- Fix hardcoded API key in main.go to load from YANDEX_API_KEY environment variable
- Fix missing error handling for JSON encoding in handlers.go RouteGeoJSON function
- Fix incorrect redis.Nil handling in cache/store.go CacheAside.Exists method
- Fix incorrect error return type in station_status.go updateStationStatus to return newStatus instead of empty string

internal/storage/transfer_rules.go

@@ -2,8 +2,8 @@ package storage
 
 // TransferRule represents a minimum connection time rule.
 type TransferRule struct {
-	RuleKey      string `json:"rule_key"`
-	MinTransferTimeMinutes int  `json:"min_transfer_time_minutes"`
+	RuleKey                string `json:"rule_key"`
+	MinTransferTimeMinutes int    `json:"min_transfer_time_minutes"`
 }
 
 // TransferRuleMap is a lookup map for MCT values.
@@ -42,4 +42,4 @@ func ExtractBaseKey(ruleKey string) string {
 }
 
 // DefaultMCT is the default minimum connection time in seconds (30 minutes).
-const DefaultMCT = 1800 // 30 minutes
+const DefaultMCT = 1800 // 30 minutes