Add municipal receipt module and convert navbar to sidebar

- New module: Municipalidad de Belén receipt extraction via pdftotext+regex
  - Backend: MunicipalReceipt + WaterMeterReading models, upload/list/detail/water-consumption endpoints
  - Auto-creates budget Transaction on upload (duplicate-safe via reference)
  - Frontend: ServiciosMunicipales page with summary cards, water consumption bar chart, receipt history, PDF upload
- Convert top navbar to left sidebar with section headers (General, Finanzas, Servicios)
  - Desktop: fixed 220px sidebar, mobile: sheet overlay
  - Grouped nav: Dashboard | Presupuesto, Salarios, Pensiones, Analytics | Municipalidad

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/App.tsx

@@ -9,6 +9,7 @@ import Budget from './pages/Budget';
 import Analytics from './pages/Analytics';
 import Salarios from './pages/Salarios';
 import Pensions from './pages/Pensions';
+import ServiciosMunicipales from './pages/ServiciosMunicipales';
 
 function ProtectedRoute({ children }: { children: React.ReactNode }) {
   const { isAuthenticated } = useAuth();
@@ -36,6 +37,7 @@ function AppRoutes() {
         <Route path="/analytics" element={<Analytics />} />
         <Route path="/salarios" element={<Salarios />} />
         <Route path="/pensions" element={<Pensions />} />
+        <Route path="/servicios-municipales" element={<ServiciosMunicipales />} />
         {/* Redirect old routes */}
         <Route path="/transactions" element={<Navigate to="/budget" replace />} />
         <Route path="/transfers" element={<Navigate to="/budget" replace />} />