graph-build-briefs

@zimdin12

Use when the user wants to regenerate the brief files (`.aify-graph/brief.{md,agent.md,onboard.md,plan.md,json}`) and unresolved categorization WITHOUT re-indexing the code graph or proposing functionality changes. Common case: user hand-edited `functionality.json` or `tasks.json` and wants briefs to reflect the change. Also fine after a `graph_index(force=true)` when you want fresh briefs immediately.