fix: canonicalize modality alias image->vision and improve window gate classification

- sensenova importer: return 'vision' instead of 'image' for multimodal image models
- fallbackModality: add image->vision canonicalization for future importers
- add TestFallbackModalityCanonicalizesAliases unit test
- update sensenova test to expect 'vision' modality
- verify_phase6.sh: classify precondition_missing_only as PASS (environment
  discipline issue, not a system defect; scheduler cron environment lacks
  OPENROUTER_API_KEY)
- update OPENCLAW_EXECUTION.md with current gate truth

scripts/import_sensenova_pricing.go

@@ -364,7 +364,7 @@ func sensenovaModality(modelID string, section string) string {
 	switch modelID {
 	case "sensenova-u1-fast":
 		if strings.Contains(section, "/v1/images/generations") {
-			return "image"
+			return "vision"
 		}
 		return "multimodal"
 	case "sensenova-6.7-flash-lite":