style: apply Biome formatting to Astro templates and CSS (#27)

- Standardize HTML/CSS formatting
- Fix template indentation
- Apply consistent style to Astro components
- Update component attributes formatting

Part of #27

src/components/MainContent.astro

@@ -1,6 +1,6 @@
 ---
-import TransactionTable from './TransactionTable.tsx';
 import type { Account } from '../types';
+import TransactionTable from './TransactionTable.tsx';
 
 interface Props {
   account: Account;