feat: rewrite check-research route for Gemini Deep Research (Task 5)

Rewrite check-research cron route to use Gemini Deep Research + Imagen 4 Fast.\n\n- Replace NotebookLM polling with pollResearch() from gemini-research.ts\n- Replace NotebookLM infographic generation with generateInfographicsForTopic() from gemini-infographics.ts\n- Infographics now generated synchronously (no more async polling step)\n- enableDeepResearch toggle: skip to enriching when disabled\n- Legacy migration handler for docs stuck in infographics_generating\n- Backward compat: GROQ query matches both researchInteractionId and researchNotebookId\n- buildResearchPayload detects full ResearchPayload shape and passes through directly\n- Net -125 lines

Author: codercatdev