Library Craft Demand

Content-free demand signal for richer part-selection tooling. Aggregates library.craft events (emitted when a4sx craft composes N parts) — no content, no ids, just how often crafts happen, how many parts they compose, and the context-size spread. Size is reported descriptively, never judged (no hardcoded 'oversized' threshold), per the size-agnostic stance. multi_source_crafts (>=2 parts) is the number that matters: build Phase-1 selection tooling once it's consistently non-trivial. Crafts by QA / test accounts (the event's actor) are excluded unless include_test=true (A0.1).