Route Groq helpers through llm-providers

[stackbilt-admin]

Summary

• routes askGroq and askGroqJson through @stackbilt/llm-providers
• keeps the existing helper API for router, titles, memory/cognition, scheduled helpers, and composite planner calls
• updates Groq tests to assert provider-factory requests instead of raw chat-completion fetches
• leaves askGroqWithLogprobs on the raw Groq endpoint because llm-providers does not expose logprob request options yet

Refs #24. This removes the common raw Groq text/JSON inference helper path; remaining raw-provider cleanup is narrowed to logprobs, composite direct Anthropic/Workers calls, and a few scheduled Workers AI helpers.

Validation

• npm run typecheck
• npx vitest run tests/groq.test.ts tests/router.test.ts tests/dispatch.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