fix: resolve lint errors in modified files

- Remove unused imports from invoice-form.tsx, sidebar.tsx, dashboard-shell.tsx
- Remove unused imports from dashboard.ts and calendar.tsx
- Fix unused parameter in invoice-calendar-view.tsx with underscore prefix
- Fix type-only import for DayButton in calendar.tsx
- All typecheck errors resolved
- Remaining lint errors are in unmodified files (pre-existing)

src/components/layout/dashboard-shell.tsx

@@ -8,7 +8,6 @@ import { Menu } from "lucide-react";
 import { Logo } from "~/components/branding/logo";
 import { Button } from "~/components/ui/button";
 import { Sheet, SheetContent, SheetTrigger } from "~/components/ui/sheet";
-import { DashboardBreadcrumbs } from "~/components/navigation/dashboard-breadcrumbs";
 
 function DashboardContent({ children }: { children: React.ReactNode }) {
     const { isCollapsed } = useSidebar();