Implement Planner Agent role and system prompt

Create the Planner agent that analyzes questions and creates execution plans.

System prompt should specify:

• Role: analyze the question and break it into actionable steps
• Output format: numbered execution plan with clear steps
• Required: identify what tools/searches are needed for each step
• Handoff: write plan to workspace.artifacts["execution_plan"] and signal completion

Example plan output for test case: 1. Search ClinicalTrials.gov for "H. pylori acne vulgaris" trials 2. Filter results by date range: Jan 2018 - May 2018 3. Extract enrollment count from matching trial 4. Return numeric value

Tools needed:

• web_search
• possibly http_get for trial details

After planning, agent should update workspace phase to "executing" and handoff to Executor.