feat: add per-group metric strip in report transaction list

Compute Sum/Count/Avg/Min/Max/First/Last per accordion group in the
report view (mirroring backend ReportMetrics.compute_metrics signed
semantics) via new computeTxnMetrics helper and a showMetrics prop on
TransactionList. Remove the now-redundant top-level metric strip from
ReportViewer and restore its Outflows/Inflows/Transactions stat cards.

src/Reports/Report.tsx

@@ -1,5 +1,15 @@
 import React, { useCallback, useEffect, useMemo, useState } from "react";
-import { Container, Box, Paper, Typography, Alert } from "@mui/material";
+import {
+  Container,
+  Box,
+  Paper,
+  Typography,
+  Alert,
+  Accordion,
+  AccordionSummary,
+  AccordionDetails,
+} from "@mui/material";
+import ExpandMoreIcon from "@mui/icons-material/ExpandMore";
 import AssessmentIcon from "@mui/icons-material/Assessment";
 import { useResource, useAppContext, formatCurrency } from "../../react-openapi";
 import { useToast } from "../ui/Toast";
@@ -103,31 +113,65 @@ export default function Report() {
 
       <GenerateReportPanel onGenerated={handleGenerated} />
 
-      <Typography variant="h6" fontWeight={700} sx={{ letterSpacing: "-0.01em", mb: 1.5 }}>
-        Saved reports
-      </Typography>
-
-      {reports !== null && reports.length === 0 ? (
-        <Paper variant="outlined" sx={{ borderRadius: 3 }}>
-          <EmptyState
-            icon={<AssessmentIcon />}
-            title="No reports yet"
-            description="Generate your first report above — pick a granularity and payee (a payee-only or wildcard config snapshots weekly, monthly and quarterly)."
-          />
-        </Paper>
-      ) : (
-        <Box sx={{ display: "flex", flexDirection: "column", gap: 2.5, mb: 4 }}>
-          <ReportList
-            reports={reports ?? []}
-            loading={loading}
-            fields={reportFields}
-            selectedId={selectedId}
-            onView={(id) => setSelectedId(id)}
-            onRegenerate={handleRegenerate}
-            onDelete={handleDelete}
-          />
-        </Box>
-      )}
+      <Accordion
+        disableGutters
+        defaultExpanded
+        sx={{
+          border: "1px solid",
+          borderColor: "divider",
+          borderRadius: 2,
+          overflow: "hidden",
+          boxShadow: "none",
+          backgroundColor: "background.paper",
+          "&:before": { display: "none" },
+          mb: 4,
+        }}
+      >
+        <AccordionSummary
+          expandIcon={<ExpandMoreIcon />}
+          sx={{
+            px: 2.5,
+            py: 1,
+            "& .MuiAccordionSummary-content": {
+              alignItems: "center",
+              gap: 1.5,
+              minWidth: 0,
+            },
+          }}
+        >
+          <Typography variant="h6" fontWeight={700} sx={{ letterSpacing: "-0.01em" }}>
+            Saved reports
+          </Typography>
+          {reports !== null && (
+            <Typography variant="caption" color="text.secondary">
+              {reports.length} report{reports.length === 1 ? "" : "s"}
+            </Typography>
+          )}
+        </AccordionSummary>
+        <AccordionDetails sx={{ px: 2.5, pb: 2.5, pt: 0 }}>
+          {reports !== null && reports.length === 0 ? (
+            <Paper variant="outlined" sx={{ borderRadius: 3 }}>
+              <EmptyState
+                icon={<AssessmentIcon />}
+                title="No reports yet"
+                description="Generate your first report above — pick a granularity and payee (a payee-only or wildcard config snapshots weekly, monthly and quarterly)."
+              />
+            </Paper>
+          ) : (
+            <Box sx={{ display: "flex", flexDirection: "column", gap: 2.5 }}>
+              <ReportList
+                reports={reports ?? []}
+                loading={loading}
+                fields={reportFields}
+                selectedId={selectedId}
+                onView={(id) => setSelectedId(id)}
+                onRegenerate={handleRegenerate}
+                onDelete={handleDelete}
+              />
+            </Box>
+          )}
+        </AccordionDetails>
+      </Accordion>
 
       {selectedId && (
         <ReportViewer