Add browser or email workout reminders

[sarthakagrawal927]

Goal

Add a reminder path for scheduled workouts.

Before implementation

Choose a delivery model that honestly matches the web product:

• Browser reminders require permission handling, persistence, and a scheduling strategy.
• Email reminders require a provider, consent and unsubscribe behavior, persistence, and production configuration.

Do not imply reliable background delivery until the selected platform can provide it. This is the only remaining item from the migrated product-status umbrella.

[sarthakagrawal927]

Closing as part of Fleet backlog triage: this project is now in maintenance mode, and this item does not meet the keep-open bar (bug, marketing/discovery, or unusually high-leverage feature). The history remains here if priorities change.