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/official_pricing_import_common.go

@@ -266,6 +266,10 @@ func fallbackModality(raw string) string {
 	if value == "" {
 		return "text"
 	}
+	switch strings.ToLower(value) {
+	case "image":
+		return "vision"
+	}
 	return value
 }