v0.6.1

Additive search release.

• ScopeFilters.path_prefixes — namespace-prefix subtree scope (weft#1270)
• RepoHit.spool_id — stable spool identity (distinct from path; spools nest), makes spool_ids reachable from results
• Facets field-vocabulary doc comment (kind/lang/author)

Dual-publishes cargo heddle-api + npm @heddleco/api. Closes #106.