Route migrated Contentful spaces through Payload CMS

[jmgasper]

What changed

• adds per-space Delivery and Preview host overrides for the default, EDU, and TopGear Contentful clients
• routes both SDK and direct Contentful requests through the selected compatibility host
• adds optional Payload write-through for EDU article votes while retaining the existing Contentful Management fallback
• configures the environment-specific Payload asset origin and permits it in image/media CSP directives
• replaces the 10 unique runtime-hardcoded Contentful assets (11 uses) with their verified assets.topcoder-dev.com / assets.topcoder.com paths
• limits the seven Thrive track-card queries to the fields needed for Article small rendering and resolved image URLs
• matches exact Thrive home, tracks, search, and article routes before the generic root Contentful route
• reuses one keep-alive HTTPS agent across server-side Contentful Delivery, Preview, and Management clients
• documents the development cutover variables and adds endpoint, query-projection, routing, and connection-pool coverage

Why

This keeps Zurich and Comcast on Contentful while allowing the three exported spaces to move to the Payload compatibility API at cms.topcoder-dev.com. Migrated binary assets are served from the dedicated S3/CloudFront hostname rather than Contentful.

The Thrive home page was also over-fetching full article bodies, waiting on an unrelated default-space CMS route, and opening a new TCP/TLS connection for each CMS request. The focused changes reduce CMS response and hydration weight without changing the rendered cards or caching personalized HTML.

Validation

• nvm use (Node 10.24.1)
• focused Jest coverage: 3 suites / 4 tests passed
• npm run lint
• npm run build
• git diff --check
• all 10 unique hardcoded asset destinations verified present after the Payload asset migration
• live exact-projection probe: seven track responses reduced from 1,707,334 bytes to 104,474 bytes (93.9%) while retaining migrated image URLs

Rollout note

The Payload asset migration completed and its idempotent replay made zero writes. Keep this PR in draft until the remaining application-level compatibility and post-deployment Thrive performance smoke tests are reviewed.