feat: add Cache TTL Override per account + bump VERSION to 0.1.83

- Account-level cache TTL override: rewrite Anthropic cache_creation
  token classification (5m↔1h) in streaming/non-streaming responses
- New DB field cache_ttl_overridden in usage_log for billing tracking
- Migration 055_add_cache_ttl_overridden
- Frontend: CacheTTL override toggle in account create/edit modals
- Ent schema regenerated for new usage_log fields

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/service/usage_log.go

@@ -46,6 +46,9 @@ type UsageLog struct {
 	UserAgent    *string
 	IPAddress    *string
 
+	// Cache TTL Override 标记（管理员强制替换了缓存 TTL 计费）
+	CacheTTLOverridden bool
+
 	// 图片生成字段
 	ImageCount int
 	ImageSize  *string