Complete comments moderation flow

[ssavutu]

Summary

• Enforce closed article comment settings on public comment submission.
• Default new public comments to pending when Akismet is not configured.
• Allow nested replies to approved reader comments while keeping parent validation scoped to the same article.
• Expand the CMS comments queue with selection, bulk moderation, restore-to-pending, soft trash, and permanent delete from trash.
• Add comment submission integration coverage behind CMS_TEST_DSN and update Swagger for the new 403 response.

Validation

• go test ./...
• go test ./internal/handlers -run CommentHTTP -v (DB-backed cases skipped locally because CMS_TEST_DSN is not set)
• npm run build in frontend
• npm run lint in frontend

Related public-site changes were committed and pushed separately to Scalene CMS-Testing (dcf17c6).