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/mutation.go

@@ -15061,6 +15061,7 @@ type UsageLogMutation struct {
 	image_count                 *int
 	addimage_count              *int
 	image_size                  *string
+	cache_ttl_overridden        *bool
 	created_at                  *time.Time
 	clearedFields               map[string]struct{}
 	user                        *int64
@@ -16687,6 +16688,42 @@ func (m *UsageLogMutation) ResetImageSize() {
 	delete(m.clearedFields, usagelog.FieldImageSize)
 }
 
+// SetCacheTTLOverridden sets the "cache_ttl_overridden" field.
+func (m *UsageLogMutation) SetCacheTTLOverridden(b bool) {
+	m.cache_ttl_overridden = &b
+}
+
+// CacheTTLOverridden returns the value of the "cache_ttl_overridden" field in the mutation.
+func (m *UsageLogMutation) CacheTTLOverridden() (r bool, exists bool) {
+	v := m.cache_ttl_overridden
+	if v == nil {
+		return
+	}
+	return *v, true
+}
+
+// OldCacheTTLOverridden returns the old "cache_ttl_overridden" field's value of the UsageLog entity.
+// If the UsageLog object wasn't provided to the builder, the object is fetched from the database.
+// An error is returned if the mutation operation is not UpdateOne, or the database query fails.
+func (m *UsageLogMutation) OldCacheTTLOverridden(ctx context.Context) (v bool, err error) {
+	if !m.op.Is(OpUpdateOne) {
+		return v, errors.New("OldCacheTTLOverridden is only allowed on UpdateOne operations")
+	}
+	if m.id == nil || m.oldValue == nil {
+		return v, errors.New("OldCacheTTLOverridden requires an ID field in the mutation")
+	}
+	oldValue, err := m.oldValue(ctx)
+	if err != nil {
+		return v, fmt.Errorf("querying old value for OldCacheTTLOverridden: %w", err)
+	}
+	return oldValue.CacheTTLOverridden, nil
+}
+
+// ResetCacheTTLOverridden resets all changes to the "cache_ttl_overridden" field.
+func (m *UsageLogMutation) ResetCacheTTLOverridden() {
+	m.cache_ttl_overridden = nil
+}
+
 // SetCreatedAt sets the "created_at" field.
 func (m *UsageLogMutation) SetCreatedAt(t time.Time) {
 	m.created_at = &t
@@ -16892,7 +16929,7 @@ func (m *UsageLogMutation) Type() string {
 // order to get all numeric fields that were incremented/decremented, call
 // AddedFields().
 func (m *UsageLogMutation) Fields() []string {
-	fields := make([]string, 0, 30)
+	fields := make([]string, 0, 31)
 	if m.user != nil {
 		fields = append(fields, usagelog.FieldUserID)
 	}
@@ -16980,6 +17017,9 @@ func (m *UsageLogMutation) Fields() []string {
 	if m.image_size != nil {
 		fields = append(fields, usagelog.FieldImageSize)
 	}
+	if m.cache_ttl_overridden != nil {
+		fields = append(fields, usagelog.FieldCacheTTLOverridden)
+	}
 	if m.created_at != nil {
 		fields = append(fields, usagelog.FieldCreatedAt)
 	}
@@ -17049,6 +17089,8 @@ func (m *UsageLogMutation) Field(name string) (ent.Value, bool) {
 		return m.ImageCount()
 	case usagelog.FieldImageSize:
 		return m.ImageSize()
+	case usagelog.FieldCacheTTLOverridden:
+		return m.CacheTTLOverridden()
 	case usagelog.FieldCreatedAt:
 		return m.CreatedAt()
 	}
@@ -17118,6 +17160,8 @@ func (m *UsageLogMutation) OldField(ctx context.Context, name string) (ent.Value
 		return m.OldImageCount(ctx)
 	case usagelog.FieldImageSize:
 		return m.OldImageSize(ctx)
+	case usagelog.FieldCacheTTLOverridden:
+		return m.OldCacheTTLOverridden(ctx)
 	case usagelog.FieldCreatedAt:
 		return m.OldCreatedAt(ctx)
 	}
@@ -17332,6 +17376,13 @@ func (m *UsageLogMutation) SetField(name string, value ent.Value) error {
 		}
 		m.SetImageSize(v)
 		return nil
+	case usagelog.FieldCacheTTLOverridden:
+		v, ok := value.(bool)
+		if !ok {
+			return fmt.Errorf("unexpected type %T for field %s", value, name)
+		}
+		m.SetCacheTTLOverridden(v)
+		return nil
 	case usagelog.FieldCreatedAt:
 		v, ok := value.(time.Time)
 		if !ok {
@@ -17745,6 +17796,9 @@ func (m *UsageLogMutation) ResetField(name string) error {
 	case usagelog.FieldImageSize:
 		m.ResetImageSize()
 		return nil
+	case usagelog.FieldCacheTTLOverridden:
+		m.ResetCacheTTLOverridden()
+		return nil
 	case usagelog.FieldCreatedAt:
 		m.ResetCreatedAt()
 		return nil