Add paginated cached resources with file upload/delete and mobile-first UI

[thughari]

Motivation

• Avoid refetching the entire resource catalog by caching paginated results so the app scales with many resources.
• Allow users to contribute files (PDF/DOC/DOCX/TXT) in addition to links and ensure uploaded files are removed from storage when deleted.
• Keep resources connected to the application after login and show ownership-aware controls for delete operations.
• Provide a clean, mobile-first UI and client-side file validation (type + 10MB limit) to improve UX.

Description

• Backend: extended CareerResource with resourceType, originalFileName, and fileSizeBytes, added CareerResourceDTO fields and a new CareerResourcePageResponse model, added paginated repository method and a GET /api/resources?page&size endpoint that returns cached pages via @Cacheable and supports anonymous/authenticated viewers.
• Backend: added POST /api/resources/upload to accept multipart file uploads and DELETE /api/resources/{id} to remove resources, implemented createResourceFromFile and deleteResource in CareerResourceService with @CacheEvict and storage cleanup via the existing StorageService (works for R2 and local mock).
• Frontend: ResourceService now uses an in-memory page cache (Map keyed by page:size), exposes getResources(page,size,forceRefresh), uploadResourceFile(...), deleteResource(...) and invalidates cache on mutations.
• Frontend UI: reworked ResourcesComponent and template for mobile-first layout, added link vs file contribution modes, client-side file type/size checks (10MB max), a “Load more” paginated flow, file metadata display and an owner-only delete button; updated unit test mocks to the paged API shape and new methods.

Testing

• npm --prefix frontend run start -- --host 0.0.0.0 --port 4200 started successfully and a mobile screenshot was captured for visual verification.
• npm --prefix frontend run test -- --watch=false --browsers=ChromeHeadless failed in this environment because a ChromeHeadless binary is not available.
• npm --prefix frontend run build failed here due to inlining Google Fonts returning HTTP 403 during the build (external resource policy in this environment).
• mvn -q test could not run in this environment because Maven could not resolve the parent POM from Maven Central (HTTP 403); component unit test mocks were updated to reflect the new paged API and added methods.

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Codex Task