fix(notion-search): drop unused _flatten_property arg + lock falsy-value behavior

Code review polish:
- Drop the unused `name` parameter from `_flatten_property` (it was
  reserved for future per-property-name special-casing but never used).
- Add a regression test pinning that checkbox=False and number=0 are
  preserved in the enriched output. The existing empty-value filter is
  `if value not in (None, [], "")` which keeps falsy-but-meaningful
  values, but the contract wasn't tested.

22/22 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

custom-skills/31-notion-organizer/code/scripts/notion_search.py

@@ -154,7 +154,7 @@ TEXT_BEARING_BLOCK_TYPES = {"paragraph", "heading_1", "heading_2", "heading_3",
                              "numbered_list_item", "to_do", "toggle"}
 
 
-def _flatten_property(name: str, prop: Dict):
+def _flatten_property(prop: Dict):
     """Flatten a Notion property to a Python value suitable for display/rerank."""
     ptype = prop.get("type")
     if ptype == "title":
@@ -224,7 +224,7 @@ def enrich_candidates(notion, candidates: List[Dict]) -> List[Dict]:
         for name, prop in properties.items():
             if prop.get("type") == "title":
                 continue
-            value = _flatten_property(name, prop)
+            value = _flatten_property(prop)
             if value not in (None, [], ""):
                 flat_props[name] = value
         excerpt = _fetch_excerpt(notion, c["id"])