Reports frontend — spec-driven generate form, sliceable viewer, dimension bars (#16)

# MR: Reports frontend — spec-driven generate form, sliceable viewer, dimension bars

**Branch:** `cached-reporting` → **Target:** `main`

## Summary

Reports UI rebuilt to treat the backend OpenAPI spec as the source of truth: the
generate-report form renders generically from `ReportQuery`, and the viewer displays
API-computed metrics verbatim instead of recomputing them client-side.

## Changes

### react-openapi (library)
- `MultiEnumField` renderer for array-of-enum fields; dispatch branch in
  `FormFieldRenderer`
- `useFkFieldOptions` hook + `FKFieldConfig.value` (FK options keyed by a non-PK
  field — accounts resolve by `name`)
- `FieldConfig.defaultValue` seeding in `extractFields`; enum lift for
  `items.enum` arrays; sanitize-payload bypasses FK resolution when `fk.value` is set

### Reports page
- **GenerateReportPanel**: rewritten (~275 → ~110 lines) — fields extracted from the
  served `ReportQuery` schema (labels, order, defaults, multi-enum, account picker);
  server-side validation only
- **ReportViewer**:
  - Period groups built from cube buckets keyed by canonical `period_id`; buckets
    merged per period (disjoint slices), txn ids deduped
  - Cards/bars/metric strips read `metrics` verbatim (outflows/inflows/sum/count/
    avg/min/max/cadence/frequency); Net = one subtraction at render
  - Dimension-switchable bar strip (Period / Payees / Tags): segmented pill control
    with sliding indicator; pills disabled when the report has ≤1 distinct value;
    top-10 bars in a fixed view paged by chevrons (hidden scrollbar)
  - Active dim requests the full distribution via `payee=*` / `tags=*` when its own
    filter is unselected; explicit selections always slice normally
- **TransactionList**: shared component with optional `groups` prop (API periods +
  metrics) used by the viewer; Expense page keeps the client-side fallback path;
  group strip shows Sum · Avg · Min · Max · Cadence (or Frequency /day when
  cadence < 1)

### Fixes
- Strict DD-MM-YYYY parsing (`parseOccurredAt`) in period merges and date ordering —
  `new Date()` mis-read dates as MM-DD-YYYY and corrupted merged cadence
  (Aug Zomato: 12.89 days displayed vs 0.76 actual)
- Bar widths magnitude-based so all-outflow slices render at proper width

Reviewed-on: #16
Co-authored-by: Vishesh 'ironeagle' Bangotra <aetoskia@gmail.com>
Co-committed-by: Vishesh 'ironeagle' Bangotra <aetoskia@gmail.com>

src/common/components/StatCard.tsx

@@ -0,0 +1,26 @@
+import { Paper, Typography } from "@mui/material";
+
+interface StatCardProps {
+  label: string;
+  value: string;
+  color?: string;
+  hint?: string;
+}
+
+export function StatCard({ label, value, color, hint }: StatCardProps) {
+  return (
+    <Paper variant="outlined" sx={{ p: 2.5, borderRadius: 3, flex: 1, minWidth: 180 }}>
+      <Typography variant="caption" color="text.secondary" sx={{ textTransform: "uppercase", letterSpacing: "0.05em" }}>
+        {label}
+      </Typography>
+      <Typography variant="h5" fontWeight={700} sx={{ mt: 0.5, letterSpacing: "-0.02em", color }}>
+        {value}
+      </Typography>
+      {hint && (
+        <Typography variant="caption" color="text.secondary">
+          {hint}
+        </Typography>
+      )}
+    </Paper>
+  );
+}