refactor: rename share URL path from location to bills-due

- Renamed directory: app/[locale]/share/location -> app/[locale]/share/bills-due
- Updated all URL references in web-app (billActions, locationActions, ViewBillCard)
- Updated all URL references in email-worker templates (4 email templates)
- Updated documentation in sprints/email-worker.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

web-app/app/ui/ViewBillCard.tsx

@@ -167,7 +167,7 @@ export const ViewBillCard: FC<ViewBillCardProps> = ({ location, bill, shareId })
                 }
 
                 <div className="text-right">
-                    <Link className="btn btn-neutral ml-3" href={`/share/location/${shareId || locationID}`}>{t("back-button")}</Link>
+                    <Link className="btn btn-neutral ml-3" href={`/share/bills-due/${shareId || locationID}`}>{t("back-button")}</Link>
                 </div>
 
             </div>