fix: address code review findings

internal/cache/preferences.go

@@ -105,7 +105,7 @@ func (p *Preferences) AddSavedCity(ctx context.Context, userID, cityCode, cityNa
 		Date:    "",
 		Request: "",
 	}
-	if err := p.store.Set(ctx, cacheKey, data, CityTTL); err != nil {
+	if err := p.store.Set(ctx, cacheKey, data, PreferenceTTL); err != nil {
 		return err
 	}
 
@@ -148,7 +148,7 @@ func (p *Preferences) RemoveSavedCity(ctx context.Context, userID, cityCode stri
 		return err
 	}
 
-	return p.store.Set(ctx, key, data, CityTTL)
+	return p.store.Set(ctx, key, data, PreferenceTTL)
 }
 
 // GetSearchHistory returns the user's search history.
@@ -217,7 +217,7 @@ func (p *Preferences) AddSearchHistory(ctx context.Context, userID, fromCity, to
 		return err
 	}
 
-	if err := p.store.Set(ctx, key, data, CityTTL); err != nil {
+	if err := p.store.Set(ctx, key, data, PreferenceTTL); err != nil {
 		return err
 	}
 
@@ -260,7 +260,7 @@ func (p *Preferences) RemoveOldSearchHistory(ctx context.Context, userID string,
 		return err
 	}
 
-	if err := p.store.Set(ctx, key, data, CityTTL); err != nil {
+	if err := p.store.Set(ctx, key, data, PreferenceTTL); err != nil {
 		return err
 	}
 

internal/cache/store.go

@@ -147,6 +147,9 @@ const (
 
 	// SearchFarTermTTL is the time-to-live for search results with far-term dates (7 days).
 	SearchFarTermTTL = 7 * 24 * time.Hour
+
+	// PreferenceTTL is the time-to-live for user preferences (7 days).
+	PreferenceTTL = 7 * 24 * time.Hour
 )
 
 // GetCityKey returns the cache key for a city code.