Add recurring expenses with active nav tab highlighting

- Add RecurringExpense model to Prisma schema with migration
- Add lib/recurring-expenses.ts: CRUD + virtual projection per month
- Add /recurring-expenses API routes (GET, POST, PATCH, DELETE)
- Merge projected recurring expenses into dashboard totals and expense list
- Add RecurringExpenseManager component to /add-expense page
- Show amber "Recurring" badge on projected items; hide edit/delete for them
- Highlight active nav tab using usePathname() with hover state
- Fix Turbopack/Prisma stub issue by adding serverExternalPackages to next.config.ts
- Clear stale Turbopack stub in Dockerfile before each build

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

src/app/add-expense/page.tsx

@@ -1,4 +1,5 @@
 import { ExpenseWorkspace } from "@/components/expense-workspace";
+import { RecurringExpenseManager } from "@/components/recurring-expense-manager";
 import { CATEGORY_OPTIONS } from "@/lib/categories";
 
 export const metadata = {
@@ -16,6 +17,8 @@ export default function AddExpensePage() {
         </p>
       </header>
 
+      <RecurringExpenseManager categoryOptions={CATEGORY_OPTIONS.map((option) => ({ ...option }))} />
+
       <ExpenseWorkspace categoryOptions={CATEGORY_OPTIONS.map((option) => ({ ...option }))} />
     </div>
   );