Phase G: Add Budgeting and Year-End Close

Budgeting:
- Budget + BudgetLine entities with Jan–Dec monthly columns per GL account
- BudgetsController: Index, Create, Edit, SetDefault, Copy, Delete
- Copy action rolls a budget forward to a new fiscal year
- Budget vs. Actual report (BudgetVsActual): compares monthly budget amounts to
  real P&L by calling GetProfitAndLossAsync once per month; variance shown as
  favorable/unfavorable; year + budget selectors in header
- Views: Budgets/Index, Create, Edit with inline annual totals via budget-edit.js
- Nav link + report card on Landing

Year-End Close:
- YearEndClose entity records each closed year + JE reference for audit trail
- AccountsController.YearEndClose GET (history + form) + CloseYear POST
- Close zeroes all Revenue and Expense/COGS account balances into Retained Earnings
  via IAccountBalanceService and posts a supporting JE dated Dec 31
- Idempotency: rejects attempt to close an already-closed year
- Pre-close checklist in view to guide the workflow
- Nav link under Finance

Migration AddBudgetsAndYearEndClose applied

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

src/PowderCoating.Web/Views/Shared/_Layout.cshtml

@@ -1150,6 +1150,14 @@
                             <i class="bi bi-building-gear"></i>
                             <span>Fixed Assets</span>
                         </a>
+                        <a asp-controller="Budgets" asp-action="Index" class="nav-link">
+                            <i class="bi bi-pie-chart"></i>
+                            <span>Budgets</span>
+                        </a>
+                        <a asp-controller="Accounts" asp-action="YearEndClose" class="nav-link">
+                            <i class="bi bi-calendar-check"></i>
+                            <span>Year-End Close</span>
+                        </a>
                         <a asp-controller="RecurringTemplates" asp-action="Index" class="nav-link">
                             <i class="bi bi-arrow-repeat"></i>
                             <span>Recurring Transactions</span>