fix(engines): cap Brave API offset to 9 to avoid 422 error

Brave API only supports offset values 0-9. When pageno > 1 with
resultsPerPage=20, offset exceeded this limit causing 422 errors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/engines/braveapi.go

@@ -80,10 +80,15 @@ func (e *BraveEngine) Search(ctx context.Context, req contracts.SearchRequest) (
 		return contracts.SearchResponse{Query: req.Query}, nil
 	}
 
+	// Brave API only supports offset values 0-9 (first page of results).
+	// Paginating beyond the first page is not supported by Brave.
 	offset := 0
 	if req.Pageno > 1 {
 		offset = (req.Pageno - 1) * e.resultsPerPage
 	}
+	if offset > 9 {
+		offset = 9
+	}
 
 	args := url.Values{}
 	args.Set("q", q)