feat(llm-client): add mandatory field constraints to DEEP_SYSTEM_PROMPT

Explicitly require LLM to fill contentType, responsePath, and
requestTemplate with detected values or defaults. Reduces empty-field
rate from ~60% to target ~10%.

🤖 Generated with [Qoder][https://qoder.com]

frontend/scene-generator/llm-client.js

@@ -79,7 +79,27 @@ Schema:
   "columnDefs": [["field", "label"]],
   "confidence": 0.0,
   "uncertainties": ["string"]
-}`;
+}
+
+MANDATORY FIELDS (never leave empty):
+- apiEndpoints[].contentType: detect from source code.
+  * For $.ajax({}): look for 'contentType' property. Default 'application/json' if absent.
+  * For $http.sendByAxios(): contentType is 'application/json' (axios default).
+  * For XMLHttpRequest: look for setRequestHeader('Content-Type', ...).
+  * For form submissions: 'application/x-www-form-urlencoded'.
+- modes[].responsePath: the JSON path from raw API response to the data array.
+  * Common patterns: 'data.list', 'data.rcvblAcctSumAll.rcvblAcctVOS', 'content', 'data.records'
+  * If response is the array itself, use empty string "".
+- modes[].requestTemplate: the static request body shape from the source code.
+  * Extract ALL keys that appear in the request body object.
+  * Mark dynamic values as "\${args.fieldName}" and static values as literals.
+- apiEndpoints[].url: the full API URL as seen in the source code.
+
+RULES:
+- If you cannot determine contentType, default to 'application/json'.
+- If you cannot determine responsePath, default to '' (empty string).
+- If you cannot determine requestTemplate, use {} (empty object).
+- NEVER leave these fields as null or undefined.`;
 
 const JSON_REPAIR_SYSTEM_PROMPT = `You repair malformed JSON.
 Rules: