Recurring invoice next_send_date is incorrect across DST boundaries

<!-- Before posting please check our "Troubleshooting" category in the docs: --> Setup • Version: v5.13.26 • Environment: ZIP / CLI / LAravel Forge Checklist • Can you replicate the issue on our v5 demo site or Yes • Have you searched existing issues? Yes • Have you reported this to Slack/forum before posting? No • Have you inspected the logs in storage/logs/laravel.log for any errors? Yes Describe the bug When a company or client is set to a timezone that observes daylight savings time, recurring invoices may receive the incorrect send time. For example, if a company is set to America/New_York, and the email send time is set to 6am, upon sending a quarterly recurring invoice on August 5, 2026 6am, Invoice Ninja will update the next send time to be November 5, 2026 5am. This is because timezone_offset() for both company and client only returns the offset for the current date, not the next send date in question. Steps To Repr…