docs: document subscribing to scheduled-refresh notifications

[mngr]

Description

Documents that the scheduled refreshes sidebar is now available on published dashboards, and that anyone who can view a dashboard can subscribe or unsubscribe themselves to a schedule's email notifications — without an editor adding them as a recipient.

Changes to docs-mintlify/docs/explore-analyze/:

• scheduled-refreshes.mdx
  • Noted in the intro <Info> box that viewing schedules and subscribing to notifications only needs view access (setting schedules up still needs Edit/Manage).
  • Expanded "Accessing scheduled refreshes" to cover opening the sidebar from a published dashboard, and what each permission level can do there (Edit/Manage → full sidebar; View only → read-only list with a subscribe toggle).
  • New "Subscribing to notifications" section: how the per-schedule subscribe/unsubscribe toggle works, that it adds/removes you from the schedule's email recipients and takes effect on the next run, and when the toggle appears (email-channel schedules with notifications on — Slack/disabled schedules have nothing to subscribe to, and the toggle always stays available if you're already subscribed so you can opt out).
• notifications.mdx
  • Added a <Tip> in the Email notifications section cross-linking the self-subscribe flow.

Notes

Docs-only change. The <Tip>/<Info>/<Warning> components and all anchor/link targets were verified against existing usage on these pages. I did not run the full Mintlify build locally.

There is minor topical overlap with #11246 (duplicating schedules) on the same two pages; the edits touch different sections, so they should merge independently.