fix: resolve majority of lint errors across codebase

- Remove unused imports from page.tsx, clients/page.tsx, invoices/page.tsx
- Remove unused imports from invoice-form.tsx, invoice-workspace.tsx
- Move CustomTooltip outside component in revenue-chart.tsx (fixes react-hooks/static-components)
- Fix type safety in umami.ts (any -> unknown)
- Fix type safety in sidebar-provider.tsx (add type assertion)
- Add no-op comments to empty fallback functions in animation-preferences-provider.tsx
- Fix type safety in invoice-workspace.tsx (any[] -> typed array)

Note: dashboard/page.tsx still has ~55 type safety warnings related to 'any' types
in stats/invoice data. These are pre-existing and would require significant refactoring
of the dashboard data flow to properly type. TypeScript compilation passes.

src/components/forms/invoice-form.tsx

@@ -1,7 +1,7 @@
 "use client";
 
 import * as React from "react";
-import { useState, useEffect, useRef } from "react";
+import { useState, useEffect } from "react";
 import { useRouter } from "next/navigation";
 import { Button } from "~/components/ui/button";
 import { Card, CardContent, CardHeader, CardTitle } from "~/components/ui/card";