EVENT-11 - Connect to CMS Backend

[oorjagandhi]

Description

Replace the mock data in the Past Events section with real data fetched from the CMS backend. The section should fetch past events on page load and pass the data through to the existing card grid, search, and filter components built in #37 and #38

Acceptance Criteria

• Past events are fetched from the confirmed CMS API endpoint on page load
• The data shape from the API matches what the card grid, search, and filter components expect — update components if there are any discrepancies
• Mock data is fully removed
• A loading state is shown while the API request is in flight, matching the Figma design (confirm with design if no loading state exists)
• If the API request fails, an error message is displayed
• Error state is visible and consistent with the rest of the page design
• Event name, date, thumbnail image, and category all render correctly from real CMS data
• Clicking a card navigates to the correct gallery page using the event ID or slug returned by the API
• Search and category filtering work correctly against real data

Additional Notes

• Confirm in #backend how the gallery page URL is constructed from the CMS data (slug vs ID)