chore: unify code formatting and remove unused code

- Apply cargo fmt to Rust code with multiline error handling
- Apply Prettier formatting to TypeScript code with trailing commas
- Unify #[allow(non_snake_case)] attribute formatting
- Remove unused ProviderNotFound error variant from error.rs
- Add vitest-report.json to .gitignore to exclude test artifacts
- Optimize readability of error handling chains with vertical alignment

All tests passing: 22 Rust tests + 126 frontend tests

src/components/UsageFooter.tsx

@@ -333,7 +333,7 @@ const UsagePlanItem: React.FC<{ data: UsageData }> = ({ data }) => {
 function formatRelativeTime(
   timestamp: number,
   now: number,
-  t: (key: string, options?: { count?: number }) => string
+  t: (key: string, options?: { count?: number }) => string,
 ): string {
   const diff = Math.floor((now - timestamp) / 1000); // 秒