feat: add recurring invoices, public links, time tracker, payments, reminders

- Recurring invoices: schedule-based auto-generation with CRUD UI at /dashboard/invoices/recurring and POST /api/cron/generate-recurring cron endpoint
- Public invoice link: generate/revoke shareable /i/[token] page for unauthenticated clients with PDF download
- Live time tracker: localStorage-persisted timer widget in invoice editor that appends a line item on stop (rounds to nearest 0.25h)
- Partial payment tracking: record payments per invoice, auto-mark paid when fully covered, balance due display
- Send reminder: email reminder via Resend with custom message dialog and last-sent indicator

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

src/lib/navigation.ts

@@ -7,6 +7,7 @@ import {
   Receipt,
   BarChart2,
   Shield,
+  RefreshCw,
 } from "lucide-react";
 
 export interface NavLink {
@@ -28,6 +29,7 @@ export const navigationConfig: NavSection[] = [
       { name: "Clients", href: "/dashboard/clients", icon: Users },
       { name: "Businesses", href: "/dashboard/businesses", icon: Building },
       { name: "Invoices", href: "/dashboard/invoices", icon: FileText },
+      { name: "Recurring", href: "/dashboard/invoices/recurring", icon: RefreshCw },
       { name: "Expenses", href: "/dashboard/expenses", icon: Receipt },
       { name: "Reports", href: "/dashboard/reports", icon: BarChart2 },
     ],