Deep research on an idea before writing a PRD. Explores existing solutions via web search, analyzes competitors, assesses technical feasibility, and optionally explores the codebase. Use when asked to "research this idea", "investigate this feature", "what already exists for X", "explore solutions for X", "do research before the PRD", "look into X", or /research. Outputs a structured research document at docs/research/{name}.md. Suggests running /prd-designer as the next step. Dependencies: WebSearch (optional).