fix(web): visible 30d chart + populate homepage analytics panels

- price-area-chart + sparkline: replace non-existent `var(--color-signal-up)`
  with proper `hsl(var(--signal-up))` (and same for -down + border +
  muted-foreground). The previous tokens resolved to undefined, leaving
  the chart line + sparkline invisible against the dark background.
- public/page: switch `currentPeriod()` from monthly (YYYY-MM) to
  quarterly (YYYY-Qn) to match the MarketIndex aggregation period —
  heatmap and district stats now find rows.
- import-market-data: add `2026-Q2` to seeded periods so the current
  quarter has data on a freshly seeded dev DB.
- new scripts/seed-bulk-listings-per-district.ts: top up the dev DB
  with 12 synthetic listings per district per 7-day window so the
  movers query (which requires >= 10 listings/district/window) has
  signal to compute against.
- update price-area-chart.spec to match new color tokens.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/app/[locale]/(public)/page.tsx

@@ -25,9 +25,15 @@ import { listingsApi, type ListingDetail } from '@/lib/listings-api';
 /* ------------------------------------------------------------------ */
 
 
+/**
+ * Heatmap + district stats are aggregated quarterly in MarketIndex
+ * (`YYYY-QN`). The previous `YYYY-MM` format never matched any row, so
+ * the heatmap and district table came back empty.
+ */
 function currentPeriod(): string {
   const now = new Date();
-  return `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, '0')}`;
+  const quarter = Math.floor(now.getMonth() / 3) + 1;
+  return `${now.getFullYear()}-Q${quarter}`;
 }
 
 /* ------------------------------------------------------------------ */