Route Workers AI helpers through llm-providers

[stackbilt-admin]

Summary

• routes router Workers AI classification through createLLMProviderFactory({ cloudflare })
• routes conversation-facts and dreaming Workers AI fallbacks through buildLLMProviderFactory(env)
• routes social engagement reply generation through the Cloudflare provider
• switches router fallback classification to a Workers AI model supported by llm-providers

Refs #24. This removes the remaining small raw Workers AI helper calls outside composite/legacy utility code.

Validation

• npm run typecheck
• npx vitest run tests/router.test.ts tests/scheduled.test.ts tests/dreaming.test.ts
• npm test
• npx charter validate
• git -c core.whitespace=blank-at-eol,blank-at-eof,space-before-tab,cr-at-eol diff --check
• npm pack --dry-run