[Feature]: Genie Spaces: Data Product detail — linked spaces section

Parent PRD

#108

What to build

Show linked Genie Spaces on the Data Product detail page, so producers can see downstream Genie usage of their products.

• Backend: Use the existing GET /api/genie-spaces/?product_id=X filter (from slice #2) to fetch spaces linked to a product. No new endpoint needed.
• Frontend: Add a new section/card on the data product detail page (data-product-details.tsx) showing linked Genie Spaces. Display: space name (clickable link to Genie Space detail), status badge, last activity date, "Open in Databricks" icon. Empty state: "No Genie Spaces created from this product."
• Placement: Below output ports section or in a new tab, consistent with the page's existing layout pattern.

Acceptance criteria

• Data product detail page shows a "Genie Spaces" section/card
• Section lists all Genie Spaces whose product_ids include this product
• Each entry shows name (linked), status badge, last activity
• "Open in Databricks" icon link per space
• Empty state displayed when no spaces exist
• Section only visible to users with Genie Spaces READ permission
• Section loads asynchronously (does not block product detail rendering)

Blocked by

• Blocked by #110 (List + Get API with product_id filter)

User stories addressed

• User story 10 (linked Genie Spaces on product detail)