State spending-report outflows and inflows separately

The ynab_spending_report 'total' was a net figure: inflows (deposits into
budget accounts) subtracted from the spending total, which the model
repeated back as spending. The report now states total outflows and
inflows separately, drops net-negative groups from the per-group list,
and computes the monthly average from outflows.

blueprints/ynab/tools.py

@@ -381,19 +381,34 @@ async def ynab_spending_report(
             GROUP BY 1 ORDER BY {order}""",
         *params,
     )
+    rows = [r for r in rows if r["spent"] > 0]
     if not rows:
         return f"No spending found from {start} to {end}."
 
-    total = sum((r["spent"] for r in rows), Decimal(0))
+    totals = await _query(
+        f"""{LINES_CTE}
+            SELECT COALESCE(-SUM(LEAST(l.amount, 0)), 0) AS outflows,
+                   COALESCE(SUM(GREATEST(l.amount, 0)), 0) AS inflows
+            FROM lines l
+            JOIN ynab_accounts a ON a.id = l.account_id
+            LEFT JOIN ynab_categories c ON c.id = l.category_id
+            WHERE {' AND '.join(conditions)}""",
+        *params,
+    )
+    outflows, inflows = totals[0]["outflows"], totals[0]["inflows"]
     top = max(1, top)
     shown = rows if group_by == "month" else rows[:top]
-    lines = [f"Spending by {group_by} from {start} to {end}: total {_usd(total)}"]
+    lines = [
+        f"Spending by {group_by} from {start} to {end}:",
+        f"- Total spending (outflows): {_usd(outflows)}",
+        f"- Inflows (deposits into budget accounts, not spending): {_usd(inflows)}",
+    ]
     lines += [f"- {r['key']}: {_usd(r['spent'])} ({r['n']} txns)" for r in shown]
     if len(rows) > len(shown):
         rest = sum((r["spent"] for r in rows[len(shown) :]), Decimal(0))
         lines.append(f"- {len(rows) - len(shown)} others: {_usd(rest)}")
     if group_by == "month" and len(rows) > 1:
-        lines.append(f"Monthly average: {_usd(total / len(rows))}")
+        lines.append(f"Monthly average: {_usd(outflows / len(rows))}")
     return "\n".join(lines)