Introduce PlannerNode (Tool-Choice Heuristics) in 'github-conversations-research-agent`

[jonmagic]

Background

We need a node that decides whether to run semantic search, keyword search, or both.

Tasks

• Create PlannerNode (in github-conversations-research-agent):
  • Input: shared[:current_query] (string).
  • Output: shared[:next_search] = {tool:, query:, qualifiers: {repo?, author?}}.
• Simple rule set:
  • If regex /\b(repo|author|label|is|created|updated):/i matches → tool: :keyword
  • Else → tool: :semantic
• Wire flow: AskClarifyingNode → PlannerNode → RetrieverNode (rename old DeepResearch exec portion).
• Leave RetrieverNode temporarily hard-coded to semantic to keep compile green; log a TODO for next iteration.
• Inline docs: explain the heuristic and future extension.
• README: none yet (tool choice internal).

Acceptance Criteria

• In dry-run (--verbose) mode the planner logs tool: keyword when user query contains repo:; otherwise semantic.