fix(fts): fix multi-word field-restricted search query building

Fixes a critical bug in FTS query building where multi-word searches
with field restrictions incorrectly used OR between all word+field
combinations instead of requiring ALL words to match within at least
one field.

Example: searching "cute cat" in {title, tags} previously produced:
  title:cute* OR title:cat* OR tags:cute* OR tags:cat*
Which matched recipes with ANY word in ANY field.

Now produces:
  (title:cute* title:cat*) OR (tags:cute* tags:cat*)
Which requires ALL words to match within at least one field.

Also adds fallback to fuzzy search when FTS returns empty results,
improving search reliability.

Co-Authored-By: Claude <noreply@anthropic.com>

py/services/recipe_scanner.py

@@ -632,7 +632,12 @@ class RecipeScanner:
             fields = None
 
         try:
-            return self._fts_index.search(search, fields)
+            result = self._fts_index.search(search, fields)
+            # Return None if empty to trigger fuzzy fallback
+            # Empty FTS results may indicate query syntax issues or need for fuzzy matching
+            if not result:
+                return None
+            return result
         except Exception as exc:
             logger.debug("FTS search failed, falling back to fuzzy search: %s", exc)
             return None