舌象原图要求模型直接观察，去掉误导性的图片识别说明

- TcmEvidenceGuard：提示词改为直接观察附带的舌象/望诊原图并描述所见，单张不清只说明该张，不再把全部望诊判为未知
- DifyChatService：本地文字识别不可用或无文字时不再给图片附加“未取得可用原文”说明，原图照常携带
- 同步更新 TcmEvidenceGuardTaskAnalysisR37Test 断言

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/tests/TcmEvidenceGuardTaskAnalysisR37Test.php

@@ -62,8 +62,8 @@ $imageLimits = TcmEvidenceGuard::limitationsPrompt($withImages);
 guardR37($withImages['current_tongue_images']['reference_count'] === 1
     && !$withImages['current_tongue_images']['content_read']
     && !$withImages['current_tongue_images']['tongue_appearance_verified'], 'Image references never certify access or visual conclusions.');
-guardR37(str_contains($imageLimits, '引用数量不等于已访问、已读取或已确认舌质舌苔')
-    && str_contains($imageLimits, '优先核验已有附件'), 'Existing image references are acknowledged before requesting new capture.');
+guardR37(str_contains($imageLimits, '请直接观察图片')
+    && str_contains($imageLimits, '不因此把全部望诊判为未知'), 'Attached tongue images are observed directly, never dismissed as unread.');
 guardR37(TcmEvidenceGuard::assess(['chief_complaint' => '口干。', 'tongue' => '舌淡红，苔薄白。'])['missing'] === [],
     'Recorded tongue and symptoms remain complete without pulse.');
 guardR37(serialize([$current, $source]) === $frozen, 'Prompt/review never changes source facts after processing.');