fix(infinity): Use comma separator for important_kwd to preserve mult… (#12618)

## Problem

The \`important_kwd\` field in Infinity connector was using mismatched
separators:
- **Storage**: \`list2str(v)\` uses space as default separator
- **Reading**: \`v.split()\` splits by all whitespace

This causes multi-word keywords like \`\"Senior Fund Manager\"\` to be
incorrectly split into \`[\"Senior\", \"Fund\", \"Manager\"]\`.

## Solution

Use comma \`,\` as separator for both storing and reading, consistent
with:
1. The LLM output format in \`keyword_prompt.md\` (\"delimited by
ENGLISH COMMA\")
2. The \`cached.split(\",\")\` in \`task_executor.py\`

## Changes

- \`insert()\`: \`list2str(v)\` → \`list2str(v, \",\")\`
- \`update()\`: \`list2str(v)\` → \`list2str(v, \",\")\`
- \`get_fields()\`: \`v.split()\` → \`v.split(\",\") if v else []\`

## Impact

This bug affects:
- Python-level reranking weight calculation (\`important_kwd * 5\`)
- API response keyword display
- Search precision due to fragmented keywords

rag/utils/infinity_conn.py

@@ -340,7 +340,7 @@ class InfinityConnection(InfinityConnectionBase):
                     if not d.get("docnm_kwd"):
                         d["docnm"] = self.list2str(v)
                 elif k == "important_kwd":
-                    d["important_keywords"] = self.list2str(v)
+                    d["important_keywords"] = self.list2str(v, ",")
                 elif k == "important_tks":
                     if not d.get("important_kwd"):
                         d["important_keywords"] = v
@@ -429,7 +429,7 @@ class InfinityConnection(InfinityConnectionBase):
                 if not new_value.get("docnm_kwd"):
                     new_value["docnm"] = v
             elif k == "important_kwd":
-                new_value["important_keywords"] = self.list2str(v)
+                new_value["important_keywords"] = self.list2str(v, ",")
             elif k == "important_tks":
                 if not new_value.get("important_kwd"):
                     new_value["important_keywords"] = v
@@ -532,7 +532,7 @@ class InfinityConnection(InfinityConnectionBase):
                     res[field] = res["docnm"]
         if "important_keywords" in res.columns:
             if "important_kwd" in fields_all:
-                res["important_kwd"] = res["important_keywords"].apply(lambda v: v.split())
+                res["important_kwd"] = res["important_keywords"].apply(lambda v: v.split(",") if v else [])
             if "important_tks" in fields_all:
                 res["important_tks"] = res["important_keywords"]
         if "questions" in res.columns: