[theNEXlevel]

Summary

• Replace page-local MUI snackbars and transient browser alerts with a shared shadcn/Base UI toast provider, queued announcements, keyboard dismissal, and a five-second timeout.
• Add and sync the accessible notification spec, archive the completed OpenSpec change, and include the before/after review screenshots.
• Normalize enrollment and Yes/No enum values in student updates, and select only the student ID from Prisma updates to avoid deserializing legacy empty enum values.

Verification

• openspec validate --specs passed (2 specs, 0 failures).
• Chromium review of the notification provider covered live-region roles, keyboard dismissal, repeated and rapid notices, hover/focus timeout pauses, and the five-second timeout (observed about 5.3 seconds).
• Spoken screen-reader output was not verified because no screen reader was available in the environment.