Add missing ARIA labels to icon-only buttons

[hasnaintypes]

Context

Several icon-only buttons (delete, edit, close) lack aria-label attributes, making them inaccessible to screen readers.

What needs to be done

Audit components for icon-only buttons and add appropriate aria-label props:

• Sidebar toggle buttons
• Table action buttons (edit, delete)
• Modal close buttons
• Any <Button size="icon"> without a label

Implementation hints

// Before
<Button size="icon" variant="ghost" onClick={onDelete}>
  <Trash2 className="h-4 w-4" />
</Button>

// After
<Button size="icon" variant="ghost" onClick={onDelete} aria-label="Delete transaction">
  <Trash2 className="h-4 w-4" />
</Button>

Acceptance criteria

• All icon-only buttons have aria-label
• Labels are descriptive (not just "button")
• Passes pnpm check