plastic-intent-speccing

Consolidate the enriched Why (## Context, ### Decisions, ## Insights) into spec.md through a deterministic, judgment-free numbered sequence. Use when the user types the command to turn the brainstorm into a spec, asks to "write the spec", "spec this intent", "consolidate into spec.md", or the active intent is at Why with enough Decisions on record to close it out. Also fires on an indirect request that never names…