fix: FindModel reverse fuzzy match for date-suffixed model IDs

Add step between exact ID match and forward fuzzy match that checks
if registry model ID starts with the requested name. Fixes models like
'gpt-5.4-mini' not matching 'gpt-5.4-mini-2026-04-01' in registry.

internal/models/registry.go

@@ -56,7 +56,16 @@ func (r *ModelRegistry) FindModel(modelID string) *ModelMetadata {
 		}
 	}
 
-	// Try fuzzy matching (e.g. gpt-4o-2024-05-13 matching gpt-4o)
+	// Try reverse fuzzy matching (e.g. 'gpt-5.4-mini' matching 'gpt-5.4-mini-2026-04-01')
+	for _, provider := range r.Providers {
+		for id, model := range provider.Models {
+			if strings.HasPrefix(id, modelID) {
+				return &model
+			}
+		}
+	}
+
+	// Try fuzzy matching (e.g. 'gpt-4o-2024-05-13' matching 'gpt-4o')
 	for _, provider := range r.Providers {
 		for id, model := range provider.Models {
 			if strings.HasPrefix(modelID, id) {