Fix bug in deletion of marked notifications

[henryk86]

Summary

This PR fixes the completely broken notification persistence flow and cleans up several related issues that caused notifications to randomly disappear, duplicate, fail deletion, or restore corrupted state from localStorage.

Fixed

• notifications not persisting after reload/import
• broken UUID handling in tables/actions
• delete actions failing randomly
• stale provider state overwriting imported notifications
• invalid legacy date handling

Changes

Persistence

• unified initial load + reload behavior
• fixed provider state desync after localStorage imports
• added explicit notification reload support

UUID handling

• removed synthetic row IDs
• table/actions now use real notification UUIDs
• auto-repair for missing or duplicate UUIDs

Date fixes

• normalized invalid legacy timestamps
• fixed dayjs date filtering
• corrected start/end-of-day range handling

Import/export

• imported notifications are now normalized
• legacy notification payloads migrate automatically
• import success notifications no longer overwrite persisted state

Limits

• hard limit of 500 stored notifications
• automatic trimming of oldest entries

Result

Notifications now actually:

• persist correctly
• survive reloads/imports
• delete reliably
• maintain valid UUIDs/dates
• stop growing infinitely in localStorage