feat: create actual News/Event/Resource content on country request ap…

[Rashed99Azm]

Description
Currently, when an admin approves a state representative's content request (News, Event, or Resource), the request status is updated to Approved but no actual content is created in the news, events, or resources tables. The data remains trapped in the country_content_requests table with no effect.
This PR closes the gap by introducing a domain event handler that, on approval, creates and publishes the corresponding content aggregate in the same transaction.
Changes

1. Entity enhancement — Added ProposedCategoryId to CountryContentRequest so resource category is captured at submission time. Also fixed a bug where Event.FeaturedImageAssetId was validated but discarded.
2. New handler — CountryContentRequestApprovedContentHandler subscribes to CountryContentRequestApprovedEvent (via MediatR) and:

• Resource → Resource.Draft(...) + .Publish()
• News → News.Draft(...) + .Publish()
• Event → Event.Schedule(...)
  Because domain events are dispatched inside EF's SavingChangesAsync interceptor, the new content is persisted atomically with the approval status update — no dual-write window.

3. Migration — Adds proposed_category_id column to country_content_requests.
   Related user stories

• US050 — Process Country Request (approve → create actual content)
  Checklist
• Source projects build with 0 warnings, 0 errors
• No manual DI registration needed (MediatR scans assembly)
• Migration generated