[FULLSTACK] Integrate Posts collection with frontend and insert placeholder data

[sswez02]

Is your feature request related to a problem? Please describe.

The Posts collection exists in Payload but the frontend News page still displays hardcoded content. We need to connect the frontend to the Payload API so it renders real post data from the CMS.

Describe the solution you'd like

• Populate the Posts collection with placeholder data (linked in #important-info)
• Fetch posts from the Payload API on the News page
• Implement category filtering (blog, alumni_story, interview, scholarships, newsletters, education)
• Individual post pages should use the slug field for their URL route
• Render rich text body, photos array, author, published date, and category tag

Describe alternatives you've considered

Additional context

Payload local API docs: https://payloadcms.com/docs/local-api/overview

Suggested branch name: feat/integrate-posts
Suggested commit message: feat: integrate posts collection with frontend

BEFORE MERGING

• Integration test written for services
• Schemas annotated if adding new models
• Code generation run (hint: pnpm generate:types)
• Appropriate mocks created where possible
• PR Reviewed (For non-trivial changes)
• Changes tested after rebasing on master or merging in master (hint: git fetch origin master:master, then git rebase master or git merge master)
• All required PR checks passing