Rename ArchiveItem/archive-item to KnowledgeItem/knowledge-item throughout the codebase

[burkkyy]

Context

TK-84 renamed the user-facing Knowledge Item route path segment from archive-items to knowledge-items (see PR for TK-84), since the UI has called these "Knowledge Items" for a while (breadcrumbs, labels, etc.) while the URL and code still said "archive item(s)."

That PR only changed the route path strings to fix the URLs. Everything else still uses the old archive-item naming, which is now inconsistent with both the UI copy and the URLs:

• Route names: archive-items/ArchiveItemListPage, archive-items/ArchiveItemPage, etc. (web/src/routes.ts)
• Vue components/pages: web/src/pages/archive-items/*, web/src/components/archive-items/* (e.g. ArchiveItemListPage.vue, ArchiveItemCard.vue, ArchiveItemNewForm.vue)
• Frontend API module: web/src/api/archive-items-api.ts
• Backend models: api/src/models/archive-item.ts, archive-item-file.ts, archive-item-audit.ts, archive-item-category.ts, information-sharing-agreement-archive-item.ts, archive-item-information-sharing-agreement-access-grant.ts
• Backend controllers/services/serializers under api/src/controllers, api/src/services, api/src/serializers referencing archive-item(s)
• API routes (/api/archive-items... in api/src/router.ts)
• DB table/column names (archive_items, archive_item_id, etc.) — would need a migration, and is the riskiest part of this rename

Scope

Out of scope for TK-84, which only needed the public-facing URL fixed. This issue is to track doing the full rename for consistency, once someone can properly scope how far it goes (just naming in code, vs. also renaming DB tables/columns and API endpoints).

Suggested order (if pursued)

1. Frontend: component/page file names, route names, API module, prop/variable names
2. Backend: model/controller/service/serializer file and symbol names, /api/archive-items → /api/knowledge-items endpoints
3. Database: table/column rename migration (highest risk, needs careful review of any external consumers)