fix: data quality query and suppression fallback in recommendation worker

- Fix _DATA_QUALITY_QUERY: remove nonexistent d.source_id/s.source_class,
  use d.source_type directly
- Fix LIMIT 1 applied after jsonb expansion by restructuring as CTE
- Fix fallback build_quality_context_from_summary returning empty
  source_types which always triggered LOW_SOURCE_DIVERSITY suppression
- Update test to reflect corrected fallback behavior

services/recommendation/suppression.py

@@ -107,7 +107,8 @@ def build_quality_context_from_summary(
 
     This is a fallback when full document-level quality metrics aren't
     available. It uses the trend summary's evidence counts and confidence
-    as proxies.
+    as proxies.  We assume at least one source type contributed so that
+    the fallback does not automatically trigger LOW_SOURCE_DIVERSITY.
     """
     total = len(summary.top_supporting_evidence) + len(summary.top_opposing_evidence)
     return DataQualityContext(
@@ -116,7 +117,7 @@ def build_quality_context_from_summary(
         failed_documents=0,
         avg_extraction_confidence=summary.confidence,
         newest_evidence_at=summary.generated_at,
-        source_types=set(),
+        source_types={"unknown"},
     )