fix(rag/prompts): Restructure metadata extraction rules for precision (#12360)

### What problem does this PR solve?

- Simplified and consolidated extraction rules
- Emphasized strict evidence-based extraction only
- Strengthened enum handling and hallucination prevention
- Clarified output requirements for empty results

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

rag/prompts/meta_data.md

@@ -1,14 +1,11 @@
-## Role: Metadata extraction expert
+## Role: Metadata extraction expert.
-## Constraints:
+## Rules:
- - Core Directive: Extract important structured information from the given content. Output ONLY a valid JSON string. No Markdown (e.g., ```json), no explanations, and no notes.
+ - Strict Evidence Only: Extract a value ONLY if it is explicitly mentioned in the Content. 
- - Schema Parsing: In the `properties` object provided in Schema, the attribute name (e.g., 'author') is the target Key. Extract values based on the `description`; if no `description` is provided, refer to the key's literal meaning.
+ - Enum Filter: For any field with an 'enum' list, the list acts as a strict filter. If no element from the list (or its direct synonym) is found in the Content, you MUST NOT extract that field.
- - Extraction Rules: Extract only when there is an explicit semantic correlation. If multiple values or data points match a field's definition, extract and include all of them. Strictly follow the Schema below and only output matched key-value pairs. If the content is irrelevant or no matching information is identified, you **MUST** output {}.
+ - No Meta-Inference: Do not infer values based on the document's nature, format, or category. If the text does not literally state the information, treat it as missing.
- - Data Source: Extraction must be based solely on content below. Semantic mapping (synonyms) is allowed, but strictly prohibit hallucinations or fabricated facts.
+ - Zero-Hallucination: Never invent information or pick a "likely" value from the enum to fill a field.
-
+ - Empty Result: If no matches are found for any field, or if the content is irrelevant, output ONLY {}. 
-## Enum Rules (Triggered ONLY if an enum list is present): 
+ - Output: ONLY a valid JSON string. No Markdown, no notes.
- - Value Lock: All extracted values MUST strictly match the provided enum list.
- - Normalization: Map synonyms or variants in the text back to the standard enum value (e.g., "Dec" to "December").
- - Fallback: Output {} if no explicit match or synonym is identified.
 
 ## Schema for extraction:
 {{ schema }}