Bug & tweak sprint: fix financial calculations, add quarterly report, enhance dashboard

- Fix Accounts page: include investment accounts in Est. Monthly Interest calc,
  add Fund column to investment table, split summary cards into Operating/Reserve
- Fix Cash Flow: ending balance now respects includeInvestments toggle
- Fix Budget Manager: separate operating/reserve income in summary cards
- Fix Projects: default sort by planned_date instead of name
- Add Vendors: last_negotiated date field with migration, CSV import/export
- New Quarterly Financial Report: budget vs actuals, over-budget flagging, YTD
- Enhance Dashboard: separate Operating/Reserve fund cards, expanded Quick Stats
  with monthly interest, YTD interest earned, planned capital spend

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

frontend/src/App.tsx

@@ -22,6 +22,7 @@ import { SankeyPage } from './pages/reports/SankeyPage';
 import { CashFlowPage } from './pages/reports/CashFlowPage';
 import { AgingReportPage } from './pages/reports/AgingReportPage';
 import { YearEndPage } from './pages/reports/YearEndPage';
+import { QuarterlyReportPage } from './pages/reports/QuarterlyReportPage';
 import { SettingsPage } from './pages/settings/SettingsPage';
 import { UserPreferencesPage } from './pages/preferences/UserPreferencesPage';
 import { OrgMembersPage } from './pages/org-members/OrgMembersPage';
@@ -135,6 +136,7 @@ export function App() {
         <Route path="reports/aging" element={<AgingReportPage />} />
         <Route path="reports/sankey" element={<SankeyPage />} />
         <Route path="reports/year-end" element={<YearEndPage />} />
+        <Route path="reports/quarterly" element={<QuarterlyReportPage />} />
         <Route path="settings" element={<SettingsPage />} />
         <Route path="preferences" element={<UserPreferencesPage />} />
         <Route path="org-members" element={<OrgMembersPage />} />