feat(analytics): replace budget page with spending analytics + split-adjusted amounts

- Rename 'Budget' → 'Analytics' in sidebar
- Rewrite /budget page: summary cards, recharts bar charts (monthly trend + category breakdown), 6-month trend table
- Fix analytics API to count only user's share for split transactions (CASE WHEN ts.share_percent IS NOT NULL THEN amount * share_percent / 100 ELSE amount END)
- Install recharts

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

@@ -25,10 +25,16 @@ export async function GET(req: NextRequest) {
     `SELECT
       TO_CHAR(DATE_TRUNC('month', t.transaction_date::date), 'YYYY-MM') as month,
       COALESCE(o.category_override, t.category) as category,
-      SUM(t.amount)::numeric(12,2) as total_spent,
+      SUM(
+        CASE
+          WHEN ts.share_percent IS NOT NULL THEN t.amount * ts.share_percent / 100
+          ELSE t.amount
+        END
+      )::numeric(12,2) as total_spent,
       COUNT(*)::int as transaction_count
     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
       AND t.transaction_type = 'debit'