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/monthly/route.ts

@@ -29,6 +29,7 @@ export async function GET(req: NextRequest) {
       SUM(
         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
       )::numeric(12,2) as total_spent,