Plan Elixir/Phoenix Feature

Plan a feature by spawning Elixir specialist agents, then output structured plan with checkboxes.

What Makes /phx:plan Different from /plan

1. Spawns Elixir specialist agents for research
2. Plans with [ecto], [liveview], [oban] task routing
3. Checks for Iron Law compliance in the plan
4. Includes mix compile/format/credo/test verification
5. Understands Phoenix context boundaries

Usage