feat(web-ui): expose citation-corroboration badge on halachot (X11)

- db.list_halachot: aggregate corroboration_count (distinct positive sources)
  + corroboration_negative from halacha_citation_corroboration (LEFT JOIN)
- web-ui: CorroborationBadge — 'מתוקף · N ציטוטים' at ≥2 (gold), soft single
  citation, danger badge on negative treatment; native title tooltips
- shown in ExtractedHalachotSection (per-precedent) + halacha review panel

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

mcp-server/src/legal_mcp/services/db.py

@@ -3406,9 +3406,23 @@ async def list_halachot(
                h.cites, h.confidence, h.quote_verified, h.review_status,
                h.reviewer, h.reviewed_at, h.created_at, h.updated_at,
                cl.case_number, cl.case_name, cl.court, cl.date AS decision_date,
-               cl.precedent_level
+               cl.precedent_level,
+               COALESCE(cor.corroboration_count, 0)::int AS corroboration_count,
+               COALESCE(cor.corroboration_negative, false) AS corroboration_negative
         FROM halachot h
         LEFT JOIN case_law cl ON cl.id = h.case_law_id
+        LEFT JOIN (
+            SELECT halacha_id,
+                   count(DISTINCT COALESCE(citing_case_law_id::text,
+                         citing_decision_id::text, source_citation_id::text))
+                     FILTER (WHERE treatment IN ('followed','explained'))
+                     AS corroboration_count,
+                   bool_or(treatment IN
+                     ('distinguished','criticized','questioned','overruled'))
+                     AS corroboration_negative
+            FROM halacha_citation_corroboration
+            GROUP BY halacha_id
+        ) cor ON cor.halacha_id = h.id
         {where_sql}
         ORDER BY h.case_law_id, h.halacha_index
         LIMIT ${idx} OFFSET ${idx + 1}