feat: polish invoice editor and viewer UI with custom NumberInput

component

- Create custom NumberInput component with increment/decrement buttons
- Add 0.25 step increments for hours and rates in invoice forms
- Implement emerald-themed styling with hover states and accessibility
- Add keyboard navigation (arrow keys) and proper ARIA support
- Condense invoice editor tax/totals section into efficient grid layout
- Update client dropdown to single-line format (name + email)
- Add fixed footer with floating action bar pattern matching business
  forms
- Redesign invoice viewer with better space utilization and visual
  hierarchy
- Maintain professional appearance and consistent design system
- Fix Next.js 15 params Promise handling across all invoice pages
- Resolve TypeScript compilation errors and type-only imports

src/lib/navigation.ts

@@ -0,0 +1,36 @@
+import {
+  Settings,
+  LayoutDashboard,
+  Users,
+  FileText,
+  Building,
+} from "lucide-react";
+
+export interface NavLink {
+  name: string;
+  href: string;
+  icon: React.ComponentType<{ className?: string }>;
+}
+
+export interface NavSection {
+  title: string;
+  links: NavLink[];
+}
+
+export const navigationConfig: NavSection[] = [
+  {
+    title: "Main",
+    links: [
+      { name: "Dashboard", href: "/dashboard", icon: LayoutDashboard },
+      { name: "Clients", href: "/dashboard/clients", icon: Users },
+      { name: "Businesses", href: "/dashboard/businesses", icon: Building },
+      { name: "Invoices", href: "/dashboard/invoices", icon: FileText },
+    ],
+  },
+  {
+    title: "Account",
+    links: [
+      { name: "Settings", href: "/dashboard/settings", icon: Settings },
+    ],
+  },
+];