Batch-create tracked competitors

Creates up to 50 competitors in one call. Used by the suggestion-accept flow to record each entry's source, rationale, and confidence. The batch is best-effort, bounded by the organization's 50-competitor cap: entries beyond the remaining capacity are dropped, an entry whose name is already tracked (case-insensitive) returns the existing competitor unchanged, and blank names are skipped — so the response can be shorter than the request and can contain rows that were not newly created.