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_fts_index.py

@@ -509,21 +509,20 @@ class RecipeFTSIndex:
         if not fields:
             return term_expr
 
-        # Build field-restricted query with OR between fields
+        # Build field-restricted query where ALL words must match within at least one field
         field_clauses = []
         for field in fields:
             if field in self.FIELD_MAP:
                 cols = self.FIELD_MAP[field]
                 for col in cols:
-                    # FTS5 column filter syntax: column:term
-                    # Need to handle multiple terms properly
-                    for term in prefix_terms:
-                        field_clauses.append(f'{col}:{term}')
+                    # Create clause where ALL terms must match in this column (implicit AND)
+                    col_terms = [f'{col}:{term}' for term in prefix_terms]
+                    field_clauses.append('(' + ' '.join(col_terms) + ')')
 
         if not field_clauses:
             return term_expr
 
-        # Combine field clauses with OR
+        # Any field matching all terms is acceptable (OR between field clauses)
         return ' OR '.join(field_clauses)
 
     def _escape_fts_query(self, text: str) -> str:

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