Podflare wildcard relay

Use this when an SDK can't be pointed at one of the per-provider
relay subdomains. Format:

    https://relay.podflare.ai/<host>/<rest-of-path>

Examples:
    https://relay.podflare.ai/api.anthropic.com/v1/messages
    https://relay.podflare.ai/registry.npmjs.org/some-package

Allowed upstream hosts (must be Cloudflare-fronted):
    api.anthropic.com
    api.groq.com
    api.mistral.ai
    api.openai.com
    api.replicate.com
    api.together.xyz
    api.x.ai
    bun.sh
    cdn.jsdelivr.net
    registry.npmjs.org
    unpkg.com

Unlisted hosts return 403. To add one, edit TARGETS in
relay-worker/src/index.ts and confirm the host has a cf-ray
header on its public edge.