fix(web): add scheduled column to i18n type definitions (#28549)

columnLabels and columnHelp in en.ts include a scheduled entry but the
Translations interface in types.ts did not declare it, causing a
TypeScript build failure in the Nix derivation. Made the field optional
since only en.ts provides it currently.

web/src/i18n/types.ts

@@ -666,6 +666,7 @@ export interface Translations {
     columnLabels: {
       triage: string;
       todo: string;
+      scheduled?: string;
       ready: string;
       running: string;
       blocked: string;
@@ -675,6 +676,7 @@ export interface Translations {
     columnHelp: {
       triage: string;
       todo: string;
+      scheduled?: string;
       ready: string;
       running: string;
       blocked: string;