fix(merchants): net spend accounting for refunds/credits

- Merchant totals now show net spend (gross debits minus refunds)
- Refund count and amount shown in profile drawer and table
- Scatter plot Y-axis uses net_spend, X-axis uses debit_count
- Per-merchant transaction history includes refunds (shown as negative)
- Monthly trend chart reflects net spend per month

src/app/api/analytics/merchants/[merchant]/route.ts

@@ -31,8 +31,10 @@ export async function GET(
       t.amount,
       t.amount_aud,
       CASE
-        WHEN ts.share_percent IS NOT NULL THEN COALESCE(t.amount_aud, t.amount) * ts.share_percent / 100
-        ELSE COALESCE(t.amount_aud, t.amount)
+        WHEN t.transaction_type IN ('refund', 'credit') THEN
+          -(CASE WHEN ts.share_percent IS NOT NULL THEN COALESCE(t.amount_aud, t.amount) * ts.share_percent / 100 ELSE COALESCE(t.amount_aud, t.amount) END)
+        ELSE
+          (CASE WHEN ts.share_percent IS NOT NULL THEN COALESCE(t.amount_aud, t.amount) * ts.share_percent / 100 ELSE COALESCE(t.amount_aud, t.amount) END)
       END::numeric(10,2) as my_amount,
       t.transaction_type,
       COALESCE(o.category_override, t.category) as category,
@@ -43,7 +45,7 @@ export async function GET(
     LEFT JOIN transaction_overrides o ON o.transaction_id = t.id
     LEFT JOIN transaction_splits ts ON ts.transaction_id = t.id AND ts.participant_id = $1
     WHERE s.owner_id = $1
-      AND t.transaction_type IN ('debit', 'fee')
+      AND t.transaction_type IN ('debit', 'fee', 'interest', 'refund', 'credit')
       AND COALESCE(o.merchant_normalized, t.merchant_normalized, t.merchant_name, t.description) = $2
     ORDER BY t.transaction_date DESC
     LIMIT 500