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/fees/route.ts

@@ -42,10 +42,12 @@ export async function GET(req: NextRequest) {
       t.transaction_type,
       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 my_amount,
       s.bank_name
     FROM transactions t
+    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
     JOIN statements s ON s.id = t.statement_id
     WHERE s.owner_id = $1