fix: normalize divine video detail responses

[rabble]

Summary

• normalize nested /api/videos/:id responses into the flat video shape used by the app
• add a regression test for the { event, stats } payload that was crashing /video/:id
• fail fast on invalid video detail payloads so the route errors cleanly instead of throwing inside npubEncode

Test Plan

• npx vitest run src/lib/divine-api.test.ts
• npx tsc --noEmit --pretty false
• npm test
• direct fetchVideo() check against the production video ID that was crashing