feat(07-01): ResearchAgent worker, trigger endpoint, main.go wiring
- internal/research/agent.go: Agent with RunOnce+Start, sanitizeQuery, interface adapters
- internal/research/agent_test.go: stub-based unit tests (sanitize, enrich, skip, empty)
- internal/ai/client.go: TierClient.TextComplete for text-only LLM calls
- internal/api/handlers/research.go: POST /api/research/trigger handler (202 Accepted)
- internal/api/router.go: researchHandler param + /api/research/trigger route
- cmd/hwlab/main.go: research agent goroutine started with 10min interval