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_test.go

@@ -58,3 +58,23 @@ func TestModelRegistry_FindModel_NotFound(t *testing.T) {
 		t.Fatal("expected nil for nonexistent model")
 	}
 }
+
+func TestModelRegistry_FindModel_ReverseFuzzy(t *testing.T) {
+	r := &ModelRegistry{
+		Providers: map[string]ProviderInfo{
+			"openai": {
+				Models: map[string]ModelMetadata{
+					"gpt-5.4-mini-2026-04-01": {ID: "gpt-5.4-mini-2026-04-01", Name: "GPT-5.4 Mini"},
+				},
+			},
+		},
+	}
+	// Reverse fuzzy: "gpt-5.4-mini" should match "gpt-5.4-mini-2026-04-01"
+	m := r.FindModel("gpt-5.4-mini")
+	if m == nil {
+		t.Fatal("expected reverse fuzzy match")
+	}
+	if m.Name != "GPT-5.4 Mini" {
+		t.Fatalf("expected GPT-5.4 Mini, got %s", m.Name)
+	}
+}