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>

scripts/import-market-data.ts

@@ -200,7 +200,7 @@ const MARKET_DATA: Record<string, DistrictPricing[]> = {
   ],
 };
 
-const PERIODS = ['2025-Q3', '2025-Q4', '2026-Q1'];
+const PERIODS = ['2025-Q3', '2025-Q4', '2026-Q1', '2026-Q2'];
 
 function randomVariation(base: number, pct: number): number {
   return base * (1 + (Math.random() - 0.5) * 2 * pct);