fix: ensure all metadata filters are processed in AND logic (#13019)

### What problem does this PR solve?

Bug: When a filter key doesn't exist in metas or has no matching values,
the filter was skipped entirely, causing AND logic to fail.

Example:
- Filter 1: meeting_series = '宏观早8点' (matches doc1, doc2, doc3)
- Filter 2: date = '2026-03-05' (no matches)
- Expected: [] (AND should return empty)
- Actual: [doc1, doc2, doc3] (Filter 2 was skipped)

Root cause:
Old logic iterated metas.items() first, then filters. If a filter's key
wasn't in metas, it was never processed.

Fix:
Iterate filters first, then look up in metas. If key not found, treat as
no match (empty result), which correctly applies AND logic.

Changes:
- Changed loop order from 'for k in metas: for f in filters' to 'for f
in filters: if f.key in metas'
- Explicitly handle missing keys as empty results


### Type of change

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

Co-authored-by: Clint-chan <Clint-chan@users.noreply.github.com>

common/metadata_utils.py

@@ -138,11 +138,15 @@ def meta_filter(metas: dict, filters: list[dict], logic: str = "and"):
                 ids.extend(docids)
         return ids
 
-    for k, v2docs in metas.items():
     for f in filters:
-            if k != f["key"]:
-                continue
+        k = f["key"]
+        if k not in metas:
+            # Key not found in metas: treat as no match
+            ids = []
+        else:
+            v2docs = metas[k]
             ids = filter_out(v2docs, f["op"], f["value"])
+
         if not doc_ids:
             doc_ids = set(ids)
         else: