feat(registry): add thinking metadata for models

internal/registry/model_registry.go

@@ -63,6 +63,9 @@ type ThinkingSupport struct {
 	ZeroAllowed bool `json:"zero_allowed,omitempty"`
 	// DynamicAllowed indicates whether -1 is a valid value (dynamic thinking budget).
 	DynamicAllowed bool `json:"dynamic_allowed,omitempty"`
+	// Levels defines discrete reasoning effort levels (e.g., "low", "medium", "high").
+	// When set, the model uses level-based reasoning instead of token budgets.
+	Levels []string `json:"levels,omitempty"`
 }
 
 // ModelRegistration tracks a model's availability