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/ent/usagelog.go

@@ -80,6 +80,8 @@ type UsageLog struct {
 	ImageCount int `json:"image_count,omitempty"`
 	// ImageSize holds the value of the "image_size" field.
 	ImageSize *string `json:"image_size,omitempty"`
+	// CacheTTLOverridden holds the value of the "cache_ttl_overridden" field.
+	CacheTTLOverridden bool `json:"cache_ttl_overridden,omitempty"`
 	// CreatedAt holds the value of the "created_at" field.
 	CreatedAt time.Time `json:"created_at,omitempty"`
 	// Edges holds the relations/edges for other nodes in the graph.
@@ -165,7 +167,7 @@ func (*UsageLog) scanValues(columns []string) ([]any, error) {
 	values := make([]any, len(columns))
 	for i := range columns {
 		switch columns[i] {
-		case usagelog.FieldStream:
+		case usagelog.FieldStream, usagelog.FieldCacheTTLOverridden:
 			values[i] = new(sql.NullBool)
 		case usagelog.FieldInputCost, usagelog.FieldOutputCost, usagelog.FieldCacheCreationCost, usagelog.FieldCacheReadCost, usagelog.FieldTotalCost, usagelog.FieldActualCost, usagelog.FieldRateMultiplier, usagelog.FieldAccountRateMultiplier:
 			values[i] = new(sql.NullFloat64)
@@ -378,6 +380,12 @@ func (_m *UsageLog) assignValues(columns []string, values []any) error {
 				_m.ImageSize = new(string)
 				*_m.ImageSize = value.String
 			}
+		case usagelog.FieldCacheTTLOverridden:
+			if value, ok := values[i].(*sql.NullBool); !ok {
+				return fmt.Errorf("unexpected type %T for field cache_ttl_overridden", values[i])
+			} else if value.Valid {
+				_m.CacheTTLOverridden = value.Bool
+			}
 		case usagelog.FieldCreatedAt:
 			if value, ok := values[i].(*sql.NullTime); !ok {
 				return fmt.Errorf("unexpected type %T for field created_at", values[i])
@@ -548,6 +556,9 @@ func (_m *UsageLog) String() string {
 		builder.WriteString(*v)
 	}
 	builder.WriteString(", ")
+	builder.WriteString("cache_ttl_overridden=")
+	builder.WriteString(fmt.Sprintf("%v", _m.CacheTTLOverridden))
+	builder.WriteString(", ")
 	builder.WriteString("created_at=")
 	builder.WriteString(_m.CreatedAt.Format(time.ANSIC))
 	builder.WriteByte(')')