Trigger finding enrichment for a skill

Starts finding enrichment for a skill named by skillId, skillVersionId, tileVersionSkillId, or explicit source coordinates. Findings default to those from the skill's latest security review; pass findings to enrich an explicit set instead. Returns the run handle to poll. Returns 422 when the findings derived from the skill's latest review are not enrichable (an explicit findings payload bypasses this check). Returns 409 when another run is already in progress for the same skill content — only enforced for skillId/skillVersionId/tileVersionSkillId targets, which resolve to a content fingerprint; concurrent source-coordinate requests have no fingerprint to guard on and are not deduplicated.