Update unread notifications on page load

[rsmithlal]

Summary

• Initialize unread notification count on page load so title and favicon reflect status immediately
• Add factories for Noticed events and notifications, linking notifications to events for cleaner test setup

Testing

• bin/codex_style_guard
• bundle exec rubocop
• bundle exec brakeman -q -w2
• bundle exec bundler-audit --update
• ENGINE_RAILS_ROOT=spec/dummy DATABASE_URL=postgis://postgres:postgres@localhost bundle exec rspec (fails: error sending request for Chrome driver)

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https://chatgpt.com/codex/tasks/task_e_68920bedeb8c8321ae9d2864bb2dd109