Remove unused cached var in config package

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/config/config_test.go

@@ -39,11 +39,6 @@ func TestSaveLoadRoundTrip(t *testing.T) {
 		t.Fatalf("Save failed: %v", err)
 	}
 
-	// Clear cache so Load reads from disk
-	mu.Lock()
-	cached = nil
-	mu.Unlock()
-
 	loaded := Load()
 	if loaded.SyncthingAPIKey != "test-key-12345" {
 		t.Errorf("API key not round-tripped: got %q", loaded.SyncthingAPIKey)