fix: resolve critical SQL and display bugs across 5 financial reports

- Fix systemic LEFT JOIN date filter bug in Balance Sheet, Income Statement,
  and Cash Flow Statement by using parenthesized INNER JOIN pattern so
  SUM(jel.debit/credit) respects date parameters
- Add Current Year Net Income synthetic equity line to Balance Sheet to
  satisfy the accounting equation (A = L + E) during open fiscal periods
- Add investment_accounts balances to Balance Sheet assets and corresponding
  equity lines for reserve/operating investment holdings
- Fix Cash Flow Statement beginning/ending cash always showing $0 by
  replacing LIKE '%Cash%' filter with account_type = 'asset'
- Fix Year-End Package HTTP 500 by replacing broken invoices.vendor_id
  query with journal-entry-based vendor payment lookup
- Fix Quarterly Report defaulting to previous quarter instead of current
- Fix Quarterly Report date subtitle off-by-one day from UTC parsing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/reports/QuarterlyReportPage.tsx

@@ -46,8 +46,8 @@ interface QuarterlyData {
 export function QuarterlyReportPage() {
   const now = new Date();
   const currentQuarter = Math.ceil((now.getMonth() + 1) / 3);
-  const defaultQuarter = currentQuarter > 1 ? currentQuarter - 1 : 4;
-  const defaultYear = currentQuarter > 1 ? now.getFullYear() : now.getFullYear() - 1;
+  const defaultQuarter = currentQuarter;
+  const defaultYear = now.getFullYear();
 
   const [year, setYear] = useState(String(defaultYear));
   const [quarter, setQuarter] = useState(String(defaultQuarter));
@@ -102,7 +102,7 @@ export function QuarterlyReportPage() {
 
       {data && (
         <Text size="sm" c="dimmed">
-          {data.quarter_label} &middot; {new Date(data.date_range.from).toLocaleDateString()} – {new Date(data.date_range.to).toLocaleDateString()}
+          {data.quarter_label} &middot; {new Date(data.date_range.from + 'T00:00:00').toLocaleDateString()} – {new Date(data.date_range.to + 'T00:00:00').toLocaleDateString()}
         </Text>
       )}