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/account.go

@@ -752,6 +752,38 @@ func (a *Account) IsSessionIDMaskingEnabled() bool {
 	return false
 }
 
+// IsCacheTTLOverrideEnabled 检查是否启用缓存 TTL 强制替换
+// 仅适用于 Anthropic OAuth/SetupToken 类型账号
+// 启用后将所有 cache creation tokens 归入指定的 TTL 类型（5m 或 1h）
+func (a *Account) IsCacheTTLOverrideEnabled() bool {
+	if !a.IsAnthropicOAuthOrSetupToken() {
+		return false
+	}
+	if a.Extra == nil {
+		return false
+	}
+	if v, ok := a.Extra["cache_ttl_override_enabled"]; ok {
+		if enabled, ok := v.(bool); ok {
+			return enabled
+		}
+	}
+	return false
+}
+
+// GetCacheTTLOverrideTarget 获取缓存 TTL 强制替换的目标类型
+// 返回 "5m" 或 "1h"，默认 "5m"
+func (a *Account) GetCacheTTLOverrideTarget() string {
+	if a.Extra == nil {
+		return "5m"
+	}
+	if v, ok := a.Extra["cache_ttl_override_target"]; ok {
+		if target, ok := v.(string); ok && (target == "5m" || target == "1h") {
+			return target
+		}
+	}
+	return "5m"
+}
+
 // GetWindowCostLimit 获取 5h 窗口费用阈值（美元）
 // 返回 0 表示未启用
 func (a *Account) GetWindowCostLimit() float64 {