feat: add Future Year Budget Planning with inflation-adjusted projections

Adds budget planning capability under Board Planning, allowing HOA boards
to model future year budgets with configurable per-year inflation rates.

Backend:
- New budget_plans + budget_plan_lines tables (migration 014)
- BudgetPlanningService: CRUD, inflation generation (per-month preservation),
  status workflow (planning → approved → ratified), ratify-to-official copy
- 8 new API endpoints on board-planning controller
- Projection engine (both board-planning and reports) now falls back to
  planned budgets via UNION ALL query when no official budget exists
- Extended year range from 3 to dynamic based on projection months

Frontend:
- BudgetPlanningPage with monthly grid table (mirrors BudgetsPage pattern)
- Year selector, inflation rate control, status progression buttons
- Inline editing with save, confirmation modals for status changes
- Manual edit tracking with visual indicator
- Summary cards for income/expense totals

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

frontend/src/App.tsx

@@ -36,6 +36,7 @@ import { InvestmentScenarioDetailPage } from './pages/board-planning/InvestmentS
 import { AssessmentScenariosPage } from './pages/board-planning/AssessmentScenariosPage';
 import { AssessmentScenarioDetailPage } from './pages/board-planning/AssessmentScenarioDetailPage';
 import { ScenarioComparisonPage } from './pages/board-planning/ScenarioComparisonPage';
+import { BudgetPlanningPage } from './pages/board-planning/BudgetPlanningPage';
 
 function ProtectedRoute({ children }: { children: React.ReactNode }) {
   const token = useAuthStore((s) => s.token);
@@ -142,6 +143,7 @@ export function App() {
         <Route path="reports/sankey" element={<SankeyPage />} />
         <Route path="reports/year-end" element={<YearEndPage />} />
         <Route path="reports/quarterly" element={<QuarterlyReportPage />} />
+        <Route path="board-planning/budgets" element={<BudgetPlanningPage />} />
         <Route path="board-planning/investments" element={<InvestmentScenariosPage />} />
         <Route path="board-planning/investments/:id" element={<InvestmentScenarioDetailPage />} />
         <Route path="board-planning/assessments" element={<AssessmentScenariosPage />} />