Add AI-assisted simulation summary prototype

[tomvothecoder]

Description

Backend + frontend for AI-assisted simulation summaries. Read-only prototype scoped to simulation detail page.

Closes #52

Backend:

• POST /assistant/simulation/{sim_id}/summary endpoint
• Structured response (summary, caveats, limitations, follow-ups, citations)
• Permission-aware metadata retrieval
• Anthropic API integration via service layer
• Pydantic schemas + service tests

Frontend:

• "Generate Summary" button on simulation detail page
• Summary display with sections: overview, key points, caveats, limitations, follow-ups
• Loading/error states
• useSimulationSummary hook

Checklist

• Code follows project style guidelines
• Self-reviewed code
• No new warnings
• Tests added or updated (if needed)
• All tests pass (locally and CI/CD)
• Documentation/comments updated (if needed)
• Breaking change noted (if applicable)

Deployment Notes (if any)

Requires ANTHROPIC_API_KEY env var set on backend.