feat(insights): analytics drill-down, fee tracking, and category improvements

- Monthly spend chart with category breakdown drill-down
- Merchant frequency and spend analytics with per-merchant history
- Subscription detection and recurring charge tracking
- Fee and interest analytics endpoint
- Expanded category list with formatCategory display helper

src/app/api/analytics/merchants/route.ts

@@ -3,12 +3,11 @@ import { getCurrentUser } from "@/lib/auth";
 import { queryRaw } from "@/lib/db";
 
 // Split-adjusted amount helper (positive for spend, negative for refunds)
+const MY_AMOUNT = `CASE WHEN ts.share_percent IS NOT NULL THEN COALESCE(t.amount_aud, t.amount) * ts.share_percent / 100 WHEN o.my_share_percent IS NOT NULL THEN COALESCE(t.amount_aud, t.amount) * o.my_share_percent / 100 ELSE COALESCE(t.amount_aud, t.amount) END`;
 const SPEND_EXPR = `
   CASE
-    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)
+    WHEN t.transaction_type IN ('refund', 'credit') THEN -(${MY_AMOUNT})
+    ELSE (${MY_AMOUNT})
   END
 `;
 
@@ -44,18 +43,18 @@ export async function GET(req: NextRequest) {
       COUNT(*) FILTER (WHERE t.transaction_type IN ('refund', 'credit'))::int as refund_count,
       COALESCE(SUM(
         CASE WHEN t.transaction_type IN ('debit', 'fee', 'interest') 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
+          ${MY_AMOUNT}
         ELSE 0 END
       ), 0)::numeric(12,2) as gross_spend,
       COALESCE(SUM(
         CASE 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
+          ${MY_AMOUNT}
         ELSE 0 END
       ), 0)::numeric(12,2) as total_refunds,
       SUM(${SPEND_EXPR})::numeric(12,2) as net_spend,
       AVG(
         CASE WHEN t.transaction_type IN ('debit', 'fee', 'interest') 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
+          ${MY_AMOUNT}
         END
       )::numeric(10,2) as avg_debit,
       MIN(t.transaction_date)::text as first_seen,